The abbreviated life of Princess Diana left behind the haunting question of what she might have become. Would she have fulfilled her potential as a global humanitarian, as suggested by her last, brilliantly achieved landmine campaign? Or would she have descended into the deluxe vagrancy of a detached celebrity princess, as suggested by her final romance with the playboy Dodi Fayed?

The lurid nature of her death 10 years ago overshadows the fact that in her final months Diana felt more alive to the potential of her public role than ever before. I met her for lunch in New York in June 1997, two months before the Paris car crash that killed her and Fayed. She was hugely excited about Tony Blair’s election win in May. She believed he had a role in mind for her as a bona fide humanitarian ambassador for Britain.

Later I learnt from Shirley Conran, a friend of hers, that in between frivolous vacations with Fayed, Diana, just 36 when she died, was plotting something she had never had before: a career. “She wanted professional fulfilment,” Conran told me. “She wanted to do something herself that would show she wasn’t an idiot.”

Diana’s privately nurtured last project, which she hoped would be in partnership with a British TV company, was to produce documentaries, on the model of the much acclaimed BBC film of her trip to Angola that highlighted her landmine campaign. She had asked friends to seek out a media coach to help improve her broadcasting skills so she could front the documentaries herself. She had already chosen the subject for her next campaign: adult illiteracy.

Would she have pulled off her evolution to an independent woman of real influence on the world’s stage? My guess is she would have. Celebrity culture, as we have seen, was moving in her direction. The political power of the monarchy had been wasting away for nearly 400 years and by Diana’s day it was in effect gone.

But the people’s princess had stumbled onto a new kind of royal power. When she hugged a seven-year-old with Aids in February 1989, grasped with bare hands the gnarled fingers of lepers later that same year, and walked across an only partially cleared Angolan minefield, she showed the latent power of the old concept of royal bounty – that the drama of humanitarian concern could be connected with the electronic nervous system of global media.

Today the tragedy of Darfur, so shamefully dependent on Hollywood’s megaphone to get air time, calls out for the Diana Effect. There is little doubt that she would have responded, beaming her travelling spotlight onto those scenes of ravaged despair in Sudan with an intensity guaranteed to mesmerise the global media. The Live 8 concert in July 2005 in Hyde Park, London, with Bono, Paul McCartney and Madonna – which succeeded in getting western governments to promise an extra $50 billion a year in Third World aid by 2010 – was an event that lacked only Diana’s presence.

To be sure, there was always an element of risk with Diana. That’s what makes her perennially fascinating. So much of what she might have become depended on that other volatile war zone: her private life. “Stand by for a mood swing, boys,” she used to say jokingly to Patrick Jephson, her private secretary, and his team.

The primal wound of her childhood abandonments and the collapse of her princess dream along with the failure of her marriage caused her, at times, to do crazy things. Her emotional neediness was forever dragging her down.

Shortly before she went away with Fayed on their ill-fated jaunt, Hasnat Khan, the Pakistani heart surgeon she adored, had ended their secret two-year affair. And the Prince of Wales had dealt her a crushing hurt by hosting a 50th birthday party for Camilla Parker Bowles at Highgrove.

Even after so many years, Diana still could not accept that her gauzy girlhood fantasy had been shattered by the tenacity of her husband’s ageing mistress. In July 1997, after watching a TV programme that positioned Parker Bowles firmly as Charles’s future consort, Diana called Debbie Frank, her astrologer, in distress. “All the grief in my past is resurfacing,” she wailed. “I feel terrible . . . so frightened and needy.” She sounded, Frank once told an interviewer, “breathy, childlike again”.

The sad truth is that in Diana’s second act she needed a man – a man who probably didn’t exist. She needed a rich, competent protector with a Gulfstream plane and a solid agenda of global concerns. A man secure enough in his own ego not to feel threatened, with inexhaustible patience for a high-strung superstar and the ability to stay discreetly in the shadows and remain unfazed by a life of constant press aggravation. A man, in short, who was the opposite of Fayed.

Jackie Onassis found such a man herself in her third act: her final beau, the businessman Maurice Tempelsman. But Onassis was always a pragmatist. Diana’s flaw – and her appeal – was that she was an incurable romantic. She always fell in love with the wrong guy.

I like to think, however, that Diana at the end of her life had come to understand what she had been put on earth for. Remember what royal walkabout photographs were like before Diana? A stiff, outstretched gloved hand, a faint smile of distant concern.

Diana gave us the princess who knelt down to talk to children at their own level, who whispered in the ears of the sick and the maimed, who greeted her own boys after trips abroad by running towards them with outstretched arms. She revived the monarchy’s understanding of something that the Queen Mother had exemplified so well during the blitz: the power of gesture.

When Diana took her famous walk in that Angolan minefield in 1997, some members of the press half-jokingly wailed that they hadn’t quite got their picture. She responded by bringing to bear all the reckless bravery she’d once used to defy the royal family – but in a much better cause.

She walked through the minefield again. This second walk was Diana’s purest synthesis of bravery, calculation and brilliantly directed media power.

It was very much a postDiana palace which ensured that after the 7/7 bombings the Queen flew the next day by helicopter from Windsor Castle to tour the wards of the Royal London hospital in Whitechapel and made a speech offering sympathy in the informal setting of the hospital’s canteen.

It was suggested recently that if Diana had lived, she would now be “competitive” with Kate Middleton, Prince William’s girlfriend. I doubt it. Middleton would not be remotely possible as a future queen without the template of Diana. Nobody wishes on William some mealy-mouthed mouse.

Thanks to Diana we now expect our princesses to be glamorous, accessible and camera-ready. Diana would have loved sponsoring the girl her son loves through the shark-infested waters of the palace naysayers. Diana was the first yummy mummy and would no doubt have eventually become the first glamour granny, upstaging all the other ageing society women at the sports days of William’s and Harry’s kids.

That’s why I remain sanguine about the future Diana never had. The role that, in the end, would have triumphed over all Diana’s difficulties was the one she treasured most: the role of mother. Few unsuitable boyfriends would have survived the disfavour of William and Harry. William had already made clear to Diana that he considered Fayed an embarrassment. Ultimately, she would have felt more protective of her eldest son’s path to the throne than she had been desirous of the queenly role for herself.

And there is no doubt that her handsome, grounded and engaging boys would have secured her restoration to her rightful place in the royal hierarchy.

“Don’t worry, Mummy,” the 14-year-old William assured her when she was told she must forfeit her title of HRH. “I will give it back to you one day when I am king.”

Diana would have wanted to make those boys proud and the greatest sadness of her loss is that she did not live to see how well her maternal instincts have served the House of Windsor.

- Tina Brown, former editor of Tatler, Vanity Fair and The New Yorker, is the author of The Diana Chronicles

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