SHE'S got purple highlights in her hair and bright blue fingernails, but to doctors at the Children's Hospital at Westmead, Demi-Lee Brennan is a one-in-6 billion miracle.

The 15-year-old liver transplant patient is the first person in the world to take on the immune system and blood type of her donor, negating the need to take anti-rejection drugs for the rest of her life. The phenomenon, which has been documented in the New England Journal of Medicine, has amazed doctors, who say they have no idea how it occurred.

Demi-Lee, of Gerroa on the South Coast, was nine when she contracted a virus that destroyed her liver. She was given less than 48 hours to live when a donated liver from a 12-year-old boy became available.