I think I had begun to know, by Christmas of 2002, that my sister's life was beginning to ebb away. But for a long time I was in denial, and chose to believe that she was in remission from the cervical cancer that had come to light in the spring of 2002. She did, indeed, make a brief recovery, but it was all too brief.

Ursula lived in New York City, where she had gone in the 1960s. She had been married, and had been happy for some years, but the marriage ended and her former husband had remarried in France. Since the 1990s, she had been alone, and for about ten years our relations were strained. We quarrelled bitterly on the day of our mother's funeral, in 1991: she called me hard-boiled and egotistical: I called her self-absorbed and neurotic.

Ursula was single, childless, living in Manhattan: I was married, with two sons, and living that frantic life of a working mother, in London. She thought my life was emotionally comfortable and secure - she saw England as a cosy place where the NHS provided for your health and nothing was never too tough or competitive. I thought her life was free from the responsibilities of having to rush around the supermarket at the end of a working day, free to explore the stimulus and openness of America.

Sibling rivalry is said to exist between sisters, and Ursula would have had good cause to resent a younger sibling. My parents initially had two sons, and then a daughter, Ursula. With that, the family seemed complete. My father adored Ursula, and for the first ten-and-a-half years of her life she had that unique father-daughter link. And then, greatly to everyone's surprise, and perhaps some embarrassment, I appeared Suddenly, this surprise new baby was the focus of all eyes, and an over-robust aunt - thinking only to tease - said to little Ursula: "Now, whose nose is put out of joint! Now, who's no longer Daddy's little girl!"

Yet, almost my first memories are of Ursula caring for me, and looking after me. Mother always seemed to be busy doing something else, and was bored child-care: it was Ursula who bathed me, washed my hair, dressed me nicely and babysat me. We didn't have our first quarrel until I was a boisterous teenager - by which time she was in her middle twenties. Ursula was quiet, thoughtful, artistic and pretty; I was noisy, brawney, extrovert, and a handful.

The years scrolled by: throughout our adult lives we were always in touch, and sometimes very close. She loved America, and insisted on my coming to New York in the 1960s, where I stayed in the Upper East Side apartment she shared with her best friend, Liz Nohilly. Ursula loved buying me clothes and little gifts; she wanted me to be chic and glamourous, instead of eccentrically pulled together, but she was soft and indulgent, never sharply critical. The rift came when she thought I no longer had time for her; this wasn't so, but the time available to a working mother can be frenetically rationed.

In 2002, she was diagnosed with cancer. Ursula had long been a devotee of Chinese herbs, and she placed too much faith in them when she was first unwell. The herbalist showed a dereliction of duty, in my opinion, by not advising her to go to a conventional doctor. I now wonder if she held back from visiting an ordinary doctor because of the expense. A doctor's visit could cost, in Manhattan, $300. She did have some insurance, but you still have to pay to see a physician initially.

She had surgery and radiation and the cancer was pronounced "contained". Her friends were wonderful, and her former husband very kind. She had a happy trip to France, where she visited Lourdes, as she desired. But by Christmas of last year, she was beginning to fail.

She shielded me from the truth for as long as possible. I was working on a book which involved visiting Germany and she held back from revealing her situation until it was impossible to disguise it any more. In March she called me on the mobile: I was sitting in my car outside the Imperial War Museum. She just said that from now on it was "palliative care only": then broke down and rang off. I just sat there, stunned, for a very long time.

Between March and June, I made five trips to New York, my stomach churning each time I boarded that Transatlantic aircraft, terrified of how I would find her: each time a little thinner and more sepulchural: yet each time sweeter and kinder and more loving to me. This need to mother me lasted right up to the end: when she was dying, at the Cabrini Hospice in East 19th Street, she sent me off to a Fifth Avenue sale, so that I should have three Lord & Taylor embroidered nighties, marked down to $17.50. They are so pretty, and I think of her each time I take them out.

After she died, I found scores of letters she had written to various business connections in America in which she sought to promote a book I had written about Ireland in 1997. The generosity with which she described my modest efforts moved me to painful feelings of regret that, really, I never did show her my full appreciation of all she had done for me. And although I spent time with her in the last months of her life, there was something cowardly in my attitude: I still pretended death was not imminent.

She died surrounded by many, many friends - Americans are very generous and often in a practical way: New York friends would visit, with chicken soup and a fistfuls of dollars, to help with the costs of drugs. Ursula was spiritual, and she was much consoled by the comforts of religion: she had the priest, a wonderful gospel minister named Joseph, a visiting Rabbi, who told an Irish joke which made everyone smile, and, at the end, a Zen Buddhist carer who literally helps people to die, Randy Phillips. The Zen philosophy is that to understand life, you must understand the importance of letting go. And you must live in each day, savouring every minute, not projecting into the future or fretting over the past.

But after she breathed her last, I went back to her apartment, and sat among her possessions, all touched with the soft perfume of her personality, and just howled. Nothing can comfort us for loss, for remembrance of things past, for the knowledge that never again, will I dial that Manhattan code, 212, and hear her voice.

I think of her most often at airports. I remember how I would call her on departing from Newark, or JFK, and she'd be so concerned that everything was all right for me, even when she herself was dying. I'd ring off with the words "Be back soon, darling sis", but in that sense, I will never be back: for it was not I, but my darling sister, who was preparing to depart, for all time.

Daily Mail 31.12.03.