Rifqa, now 17, has already undergone two operations and will have a third one on Thursday, according to a close friend and her former Orlando lawyer.
"The only reason she wants this to be known is she wants people to pray for her," said John Stemberger, who represented Rifqa in her 2009 fight to stay in Florida.
She lost that battle and was returned in October to Columbus, where she lives with a foster family.
She has been in and out of the hospital but remains under the care of the foster family, said Stemberger, who said he spoke to her last week.
Jamal Jivanjee, an ordained pastor who directs an Orlando-based ministry, also confirmed that Rifqa has cancer.
In an email to her friends and supporters, he wrote, "Her situation is very serious, and she will need the help of many people in the weeks and months ahead. . . . As soon as Rifqa heals from the major surgery that she will undergo this Thursday, it is expected that she will need to undergo several rounds of chemotherapy. . . .
"Rifqa is in desperate need of an army of supporters to know about what is occurring regarding her situation, and to pray for her healing," Jivanjee wrote.
Reached by telephone, Rifqa's father, Mohamed Bary, would not discuss his daughter's health.
Neither would Kort Gatterdam, one of her attorneys in Columbus.
Rifqa rode a bus from Columbus to Orlando in July and moved in with a husband-wife team of evangelical pastors, Blake and Beverly Lorenz. She said she ran away, saying her father or members of his mosque would kill her for converting to Christianity.
Investigators in Florida and Ohio found no proof to support those claims, and an Orange-Osceola judge ordered her back to Ohio in October, where she and her parents have continued a court battle over how she should be raised.
She turns 18 on Aug. 10. As an adult, her court battles with her father should end.
Still a problem, though, is her immigration status. She is in the country illegally, Jivanjee said, and faces the prospect of possible deportation to her native Sri Lanka.
Jivanjee said Rifqa has finished high school early and has graduated.