A seven-year-old US girl diagnosed with cancer and given 12 to 48 hours to live has defied all expectations, going on to not only beat cancer, but also to serve as a flower girl at her friend’s wedding.

Just a few months ago, leukaemia sufferer Abby Furco’s family were told she would live for no more than two days, after her body began rejecting a bone marrow transplant received as part of her treatment, Inside Edition reports .

Upon hearing the news, Sarah Rostock, 27, a cancer survivor whom Abby had befriended at Camp Fantastic — a camp for childhood cancer patients — rushed to the girl’s bedside.

Ms Rostock decided to invite Abby to her upcoming wedding as a flower girl.

"When I first asked her, we really didn't know if she was going to be there,” Ms Rostock said.

"I probably just wouldn't have had a flower girl, I guess."

In spite of the grim prognosis, Abby began to recover and survived to attend summer camp weeks later, followed by her own birthday.

To Ms Rostock’s joy, Abby was also able to attend her October 29 wedding.

"When we walked back (from the wedding), we had a nice moment of just sobbing on each other,” Ms Rostock said.

"When you reflect on all that she's been through and all that life has thrown at us, it's an emotional time.

"As long as we're both here, we'll be best friends forever."

Abby has since been declared cancer free.