A posting on the family's website for two-and-a-half-year-old Molly Campbell says she passed away early Wednesday morning.
Molly was just 28 days old in December 2010 when she was diagnosed with cancer of the white blood cells.
She fought the disease into remission for a year but relapsed last November and was transferred from B.C. Children's Hospital to St. Jude's Hospital in Memphis for intensive chemotherapy.
Her parents, brother and three sisters travelled with her but a month ago her father, David Campbell, tweeted that their talkative bubbly little girl was slipping further from them.
Since then, Molly has been intubated and battling lung infections and other complications that finally proved too much for her little body.