Rich, smart, beautiful and drunk

"A waif-like creature who inspires romantic passion" is how Cyril Connolly described Caroline Blackwood in the 1950s, when she was married to the painter Lucian Freud. Caroline was beautiful and weird, a "looker" who was also a starer, likely to say something abrupt and unpredictable, or to say nothing at all. An aristocratic bohemian and alcoholic from an early age, her grand manner fascinated or repelled people immediately: "Even in the last years,"Grey Gowrie recollects, "you could not look at anyone else in the room."

It was her fate to be inspiring, whether she wanted it or not; to Lucian Freud (who painted her four times), the photographer Walker Evans, the poet Robert Lowell (Caroline's third husband) and Connolly himself, all of whom treated her like a blank canvas for their fantasies and their art.

Eldest child of the 4th Marquess of Dufferin and Ava, Blackwood had an excitingly gothic Anglo-Irish childhood in the scruffy splendour of Clandeboye House, County Down, complete with negligent parents and a sadistic nanny. Her mother was a Guinness heiress and Blackwood never had to even think of working. Her wealth, title, open-handedness, beauty and quirky intelligence made an irresistible combination; she was never short of admirers and married a succession of brilliant, handsome, difficult men. But Blackwood herself showed every sign of being bored silly with her own attractiveness and her effect on other people and restless to do something with her life. Her solutions were having children, buying houses, drinking hugely and writing.

Blackwood was not an exceptional, prolific or even committed writer and it is a major fault of this biography that Nancy Schoenberger consistently over-praises her subject's achievement, speaking freely of "genius" and "her greatest book", etc. Blackwood had plenty of wonderful material to write from, but very little motivation. Her first book, a collection of autobiographical stories called For All That I Found There, was only published when she was 42. Several other books followed over the next 20 years, including a novel called Great Granny Webster (again, heavily autobiographical) which was shortlisted for the Booker Prize in 1977 and The Last of the Duchess, a provocative portrait of the Duchess of Windsor. She was a good writer but never really got the bit between her teeth, and to put her on a par with Lowell, idealising their marriage as one of true minds, is foolish.

Everything in Blackwood's life misfired to a greater or lesser extent, and that's where its fascination lies. Her marriages were fairly brief and very painful (especially with Lowell, who described her as "panic" to his "manic") and her drinking made her an erratic, troublesome parent to her four children, one of whom died from heroin addiction. Her astonishing beauty was over very quickly, replaced by a sort of bolshy self-neglect (including dirt and smelliness) which some people doubtless found as sexy as her former glamour, but which one former companion likened to "a radiant disease".

She was a terrible house-guest and so chaotic in hotels that she was put on some secret blacklist of undesirable clients. But she had style, and wit. Placed next to a dull architect for dinner, she told her host "He's boring. He's got a flair for it" and at her first meeting with Lowell (whom she'd been told only tolerated conversation about poetry) only broke the silence once: "I said I admired the soup. And he said, 'I think it's perfectly disgusting.' And then we had a silence."

Caroline Blackwood died in 1996 of cancer, aged 64, having been on the skids for years. There's a pathetic but comical story of her arriving in Maine in 1993 and not having the least idea what her suitcase looked like, saying impatiently to her host, Stephen Aronson, "I don't know which one is mine."

They waited until most of the bags had been claimed and Blackwood made several confident, wrong guesses, until on the third or fourth attempt Aronson "knew right away" he'd found the right one: "There was a crumpled old frock and a bottle of vodka inside. It was hers all right."