The book was published to great reviews the week before Natalie finished high school. Amazon named it the best parenting book of 2004. It was nominated for a national prize. It was translated into Lithuanian and Chinese. And then ... At 22, during the second half of her senior year of college, Natalie experienced a psychotic breakdown. In the span of a few weeks, she went from being a dazzling young adult with the world at her feet to a psychiatric patient with an arrest record. Only much later did I learn what a devastatingly common trajectory this was. Psychotic disorders nearly always emerge in late adolescence or early adulthood, with onset peaking between the ages of 18 and 25, says Thomas Insel, director of the National Institute of Mental Health. Scientists do not know why. Many researchers are focusing on abnormalities in the way the brains of people who behave psychotically develop during adolescence. Others are investigating genetics, prenatal circumstances and environmental conditions.

Some consensus has emerged around the concept that psychotic breakdowns such as Natalie's are not, as they may seem, abrupt but rather are the climax of a long build-up. In this model, they are rooted in molecular changes in the brain that begin as much as a decade before symptoms occur and progress to an end-stage psychosis in which reality surrenders to delusion, paranoia, hallucinations or other forms of disordered thinking. This idea suggests the possibility, both tantalising and controversial, that children might someday be screened for psychosis indicators the way they are screened for other health risks, with the hope of reducing the onset of psychosis much as we have reduced the prevalence of heart attacks. Natalie's symptoms probably began in her junior year of college, but - like nearly every other family member who ever talked to me about their own loved one's unravelling - I had no frame of reference to recognise them for what they were. She went a week without sleeping more than a few hours a night and seemed to have endless energy. But she was travelling abroad then and relying on caffeine to stay awake. Our family saw this as jet lag, not mania. A few months later, she reported that one of her friends had begun whispering whenever Natalie turned her head away. But the girls were on the road together in close quarters and having some spats. With no history of mental illness in the family, auditory hallucinations never crossed anyone's mind. Only half a year later - when the whisper of her friend grew into a chorus of strangers issuing commands that led to Natalie's arrests for offences such as trespassing - did the connection become apparent. Again, commonplace: The average duration of untreated psychosis in America is 70 weeks, Dr Insel says.

Like most people in the midst of psychiatric crisis, Natalie maintained that she was fine and that "everyone else is crazy". She continued to deteriorate until police officers, responding to still another call, took her to a hospital emergency room instead of to jail. After a series of psychiatric examinations and a court hearing, she was committed to the state's public psychiatric hospital. She received intensive treatment for severe bipolar disorder with psychosis until she was stable and symptom-free two months later. Natalie came home sane, revived and seemingly her vibrant old self. She moved in with me for the summer and taught me how to like grilled tofu and make scrambled eggs. She concocted the best mixed salads of my life. She filled my house with her original art, her friends and her irrepressible spirit. Mental illness was not a theme. She returned to college to restart her senior year. I saw her off with an emptier stomach but oh so much optimism. And then ... Three months later, Natalie abruptly stopped taking the medications that had kept the manic swings and auditory hallucinations at bay. Within minutes of walking through the door for a weekend at home, her delusion-loaded thinking and behaviour made it obvious that what I eventually came to think of as "the demons" were back. Natalie's relapse was worse than her first breakdown: the psychosis and stay in hospital longer, the recovery harder to achieve, the eventual medications more complicated, the resulting future not as bright.

Her second commitment to the hospital lasted 10 months, an eternity in an era where the average psychiatric stay is about five days and most people who are psychotic never get a bed at all. Thanks to the intensive care, she rebounded again, although more slowly, and finished her bachelor of fine arts degree. Her attending psychiatrist from the hospital and several staff members drove 75 miles (120 kilometres) to attend her senior art show. It was a triumph for us all. But, as is true for far too many individuals and families and professionals who live with or around untreated severe mental illness, the And thens continued. While Natalie seemed happier and more productive on medication, she missed the high of occasional mania and she hated the weight gain that is a common side-effect of the drugs she was taking. Stable, she would sometimes declare that she wasn't sick after all and didn't need medication - another very common reason people give for quitting their meds. Yet if she even inadvertently missed a few days of medication - even while receiving therapy and other forms of treatment - the demons would return, and one of the first things they would tell her was to stop taking her medicine. The second thing they would tell her was not to talk to her mom, the most powerful other influence in her life. Each time she obeyed and relapsed, she plunged into a longer free fall, hitting the ground harder, recovering more slowly and returning at a lower plateau. The final time she entered this cycle was last autumn, when she became convinced she was among the one-quarter of people with psychotic disorders whose symptoms improve only minimally or not at all with medication. There were no apparent signs of psychosis, and she seemed happy and healthy to everyone around her, but she said we couldn't see inside her head. In November, six years after her first breakdown, she announced that, because she was going to have hallucinations anyway, she was giving up her medication for good. Then 28 years old, she stopped the injectable antipsychotics and oral mood stabilisers that had helped her rebuild her life, and her mind began its final, fatal unwinding.

Natalie was a believer that treatment worked and that the mental health system needed to be reformed so other people received the kind of care she had when she was in crisis. She told her story in a documentary short last year about the criminalisation of mental illness. She dreamed of being a peer counsellor. She said she wanted to help others as she had been helped - until she became convinced that she was beyond help. In the weeks after Natalie's death, the outpouring of sympathy and grief from legions of people who have fought demons have made me keenly aware that the pain I feel from her loss is but a drop in the ocean of pain created by untreated mental illness. One woman wrote: "I have bipolar disorder and can't even begin to tell you how many people over the years have said to me, 'Be glad that is all you have. It could be worse, you could have cancer or some other terminal illness.' It saddens me that so many people do not realise that mental illness, while treatable, is not a curable disease, and can lead to death." My daughter lived more than six years with an incurable disease that filled her head with devils that literally hounded her to death, and she did it while laughing, painting, writing poetry, advocating and bringing joy to the people around her. She was the bravest person I have ever known, and her suicide doesn't change that. "Natalie will help our society to move forward," a postdoctoral fellow at Johns Hopkins Hospital wrote to me upon learning of the suicide.

"She is helping us to look at mental illness with the respect, the compassion and the dignity it deserves." I hope so. Natalie would have loved that legacy. Doris Fuller is executive director of the Treatment Advocacy Centre, a non-profit organisation in Arlington, Virginia, dedicated to eliminating barriers to treatment for people with the most severe psychiatric diseases. ❏ Support is available for those who may be distressed by phoning Lifeline 13 11 14; Mensline 1300 789 978; Kids Helpline 1800 551 800.