Ellie Merritt suffered a haemorrhage yesterday and died without having found a matching bone-marrow donor, in spite of a huge response to the appeal.
It is the second tragedy in a matter of years for her mother, Lindsay Nicholson. Ellie's father, John Merritt, a journalist for the Observer, died of leukaemia in 1992. Ellie's grandmother also died of the same bone- marrow condition.
Tony Blair's press secretary, Alastair Campbell, launched an appeal earlier this year to try to find a bone-marrow donor for Ellie. Mr Merritt had been a colleague of Mr Campbell and a close friend.
Mr Campbell said on behalf of the family: "She was a wonderful little girl who everybody hoped was pulling through but, sadly, it was not to be. Lindsay is obviously absolutely shattered."
"There was a quite extraordinary response from members of the public when Ellie's case was publicised and it is obviously tragic that she wasn't able to find a matching donor."
Ellie was being treated for her leukaemia at London's Great Ormond Street Hospital.