A successful autobiographer establishes two relationships, one with a past self and the other with a reader in the present. Janice Galloway's success in the first effort is threatened by her erratic handling of the second. All Made Up is a continuation of This is Not About Me (from 2008) and has the same intermediate status, neither quite a misery memoir nor the opposite of one. The misery is fairly undramatic, a matter of feeling unwanted (her mother mistook her beginnings for the menopause), and of physically reminding her family members of the violent father she hardly knew. Her mother left that oppressive marriage, and the two of them shared a bed until Janice was 16, because a much older sister, Cora, left her own husband (and child) to move in with them.

Saltcoats in the north of Ayrshire was a resort town for Glasgow folk, though one fairly restricted in its pleasures. Galloway conjures up the atmosphere with a loving hatred: "mongrels, demented with pleasure, rolled for days in the remains of a seal that had burst on the far North Shore". The family dynamic was perverse, with sister Cora reproducing the raging violence of the absent father while her mother made mild objections but never challenged her. Near the end of This is Not About Me, the 11-year-old Janice phones the Samaritans, theirs being the only number on display in the phone booth. She doesn't know what to say to the voice at the other end of the line. It's not that she doesn't need help, more that she has no experience of help on which to base a need for more.

In this second volume, education becomes an important theme. Galloway went to a strongly academic school at Ardrossan. She describes her daily journey to school, street by street, not once but twice. This sounds self-indulgent but works well on the page. At Ardrossan she discovered not just literature but classical music. Would a pupil today from a similar background be served so well in that department, strongly engaged with such a range of instrument and repertoire? Cora had been at the same school and had also shone, up to a certain point, the point being the moment when she discovered boys. Her abusive behaviour during Janice's schooldays can be viewed as corresponding in some infinitely distorted way to regret for her own forfeited opportunities. The most touching moment in the book is a quiet one, when Janice, sneaking into Cora's room to learn the dark arts of womanhood from her wardrobe and makeup drawer, discovers that loud, blatant, sexual Cora has quietly changed key in her early 30s, picking "another self off the rack". Her frocks, "satin-effect, dirndl-skirted, boned-bosomed", have been replaced by shifts, "sleeveless high-neck Jackie O shapes in muted navies and greens". A similar drastic change of policy has thinned out the cosmetics, replacing emerald and blood-orange with subtle enhancing tints.

The title of All Made Up is tricksy, as was also the case with This is Not About Me. In that book, the title phrase occurred a number of times, most pointedly when a primary school teacher squashed the young Janice, who had written a play, for wanting to star in it: "Writing, she said, was not about me me me." Though sometimes it must be just that, at least to start with. The title phrase appears just once in All Made Up, near the end, as part of the mother's response to being told by one of Janice's friends that he is gay. "That's all made up," she says. "It was all just stuff on the telly and Kenneth Williams. It was kidding on."

Any reader of the book, though, is going to wonder how much of it is indeed "made up". Can Galloway really remember that before she had an abortion, a third of a century ago, when the consultant (wearing a three-piece suit and a carnation) held a needle up to the light and told her to count backwards from 10, she got only as far as eight? It seems unlikely, particularly as it wouldn't have been the consultant administering an anaesthetic. But this sort of slippage isn't a major objection to All Made Up, compared with the slapdash quality of so much of its writing. Galloway dispenses with printers' marks to indicate speech, a defensible style choice as long as clarity doesn't suffer. It does here, on almost every page, with the reader struggling to disentangle speech and commentary. "Actually, I said. Being strictly factual. There is, now I come to think of it" The status of the middle sentence is beyond the reader's power to settle. In short bursts Galloway's style is vivid and fluent but she has plenty of bad habits. There are cliches either truncated ("the dim and distant", "for the foreseeable") or tweaked ("It was, at first sight, love"). One mannerism is to start with a well-known phrase and then transform it. The results are reliably unhappy. "Scales did not fall from my eyes or stitch them over insisting I was blind." The kisses of his mouth "were both sweeter than wine but more degrees proof than allowed common sense a fair fight".

She's a devoted layer of "false scents" as described by the lexicographer HW Fowler, ramshackle sentences where the intended meaning isn't the only possible one. "I defied the ugly gang to wash my face in the toilets then bite my lips till they were red." This can easily be read with "defied" meaning "dared them to", until the puzzling bit about the gang biting her lips. If "to wash" is replaced with "by washing", any ambiguity disappears.

For Virginia Woolf, "life writing" seems to have meant biography, but the phrase has expanded since her time to include a wide range of what Galloway refers to in All Made Up as "putative non-fiction", including memoirs and diaries. In the best life writing, the two halves of the formula receive equal attention, the life and the writing. "A bird never flew"  as Virginia Woolf probably didn't say, when pressing Leonard to a second pint  "on one wing."

"All happy families resemble one another, each unhappy family is unhappy in its own way." I probably won't be the only reviewer of Janice Galloway's second volume of autobiography to fall back on Tolstoy's line from Anna Karenina, even though I'm not sure I believe it. There are almost certainly books to be written about happy, well-adjusted people just getting on with life, thriving with the help of love and support from all around them. This, however, is not their time: we like our memoirs to be either shockingly salacious or else filled with woe, misfortune and tragedy. Sometimes, the three central women in All Made Up, circling each other in their claustrophobic attic digs, resemble the cast of a Harold Pinter play. Their world is constrained, their relationships seldom anything but fraught.

Galloway's first volume of memoir, This Is Not About Me, was published in 2008 and contained innumerable moments of cruelty. Janice's father comes home in a foul mood one day and tosses the family's supper (a pot of stew) into the garden. Janice's mother eventually leaves him, taking the young Janice with her. Janice's sister Cora then leaves her own husband and moves in, bringing fear and tyranny. Every morning Cora "painted on eyebrows like gull-wings" before going out to work as a secretary, but when at home, she proves capable of setting fire to Janice's hair in a fit of pique. Their mother tries to kill herself but fails, and the book ends with 11-year-old Janice on the phone to the Samaritans, after yet another small but telling act of cruelty from Cora, leaving her "a sensitive plant with a memory like a packet of razor blades". That packet is reopened in All Made Up.

One review of the first book noted  quite astonishingly  that it was "as far from a misery memoir as it's possible to imagine". Reader, beware: moments of joy are few and far between in the teenage Janice's life as her story continues, and All Made Up opens with Cora (17 years her elder) headbutting her  not for the first time. "Mum didn't pursue what had happened for long," the narrator explains. "There was no point. Stuff just happened: Cora was handy." In fact, Cora is not just handy: she is an extraordinary creation. Complex, twisted and inscrutable, when she walks into a scene fireworks are never far away.

Late on in the book, poised between school and university, Janice is loaned an evening gown by a friend. She walks into the living-room to show off to her mother, but finds Cora there too, and as proud mother prepares to capture the moment with a camera, the elder sister throws a plate of stew (yes, stew again) over Janice and the frock. Is Cora simply too bad to be true? Is she more akin to the villain in a novel or play? The titles of both volumes are ambiguous. If This Is Not About Me was not about Janice, then was it really about Cora? Or does the title imply that there is imagination at play, that memories are being moulded to suit a novelist's view of the world? Does All Made Up refer to primping and preening, or making up after a disagreement, or is it hinting at a sustained fiction?

And does it matter?

Although This Is Not About Me was shortlisted for at least one autobiography award and won a non-fiction prize, the author refers to it on her own website as "anti-memoir". Throughout All Made Up the narrator seems able to recall screeds of dialogue between mother and daughters. Is this believable, or is there a level of playful artifice at work? Galloway perhaps gives a hint when she writes about a teacher who uses a doll to demonstrate the bathing of a baby to her class: "She may have pulled off an arm as well, but that might be embroidery after the fact. Whichever is truer, the uses of borax and bicarbonate of soda as stain removers seemed tame thereafter."

While the question of veracity is intriguing, what is more important is that Galloway remains a brilliant writer, capturing mood and character, time and place, with seeming effortlessness. We watch Janice flower, becoming fascinated by language and music. She buys cheap books from Woolworth's, plus a Russian primer and a diary. This way, she can use Cyrillic script when she records her thoughts and feelings, ensuring Cora can't read them. There is a forensic level of detail throughout: a description of Cora's makeup routine, or even of a biscuit tin, can take up a whole page. And though Cora continues to bully and mistreat her sister, persisting in calling her "Creeping Jesus", Janice somehow rises above it, becoming attractive and likeable, bunking off school at 16 to have sex with a boyfriend. At 17, she has to have an abortion, at which point her mother decides she is old enough to warrant a bedroom of her own  up until then she had slept next to her mother. "Our house, I realised, had no grownups. Like children, we bickered about what was normal because we had no idea."

Cora, meantime, tosses lovers aside like cigarette-butts, but flourishes at work, "bossing juniors until they became a credit to the firm". Exotica such as Vesta curries and bolognese sauce arrive in 1970s Saltcoats, and the family eventually adds a fridge to its consumer electricals, while mother continues to dispense advice: "Self-sufficiency was the only survival tool you could count on." What moments of levity there are come with Janice's descriptions of her schoolteachers: "Miss Thomson, whose Tyrolean jumpers and ear-muff hairdo made us squeal with hilarity; whose demonstrations of mass, motion and gravity never demonstrated anything of the sort; who lost the thread and told long, rambling stories about the beauties of Elgin instead, was who the school had chosen to impart the mysteries of human sexuality to class 2Bii. It was jaw-slackening."

Towards the end of the book, Janice leaves school and begins studying music at Glasgow University. More important, perhaps, when Cora next hits her, she retaliates  and Cora never hits her again. Instead, the elder sister leaves home: "She was gone one evening when I came back off the last train and the house felt different, flushed with healing ions. We'd lived on top of the national grid for ages, now someone had switched off the plant for refurbishment . . ."

Having watched Janice age 10 years over the course of two volumes and 600 pages, the ending of All Made Up seems oddly truncated. We zip forward to Cora's decline and further examples of the unstinting adoration of her longtime suitor Daft Sandy, and are left with the puzzle of books that read like memoir while proclaiming themselves "anti-memoir", books stuffed with character and incident, any number of which may be fabrications or exaggerations  all made up, just as the author has warned us in this latest title. And, arching over the whole construct, the figure of intemperate Cora, her anger forever simmering, her sense of injustice and her own infallibility intact. If she never quite existed in reality as she is described in All Made Up, I'm still glad Janice Galloway shaped her and gave her such vibrant, hideous life.

Ian Rankin's The Impossible Dead is published by Orion.