One of my story characters has cancer. Can someone who knows cancer treatment help me make this realistic?

One of my story characters has cancer. Can someone who knows cancer treatment help me make this realistic?
The character is a girl who was diagnosed w/ cancer when she was a baby and her parent put her up for adoption because they couldn't afford expenses. Doctors thought she was terminal, but she just kept pulling through and made it to 16 yrs. old. Is this realistic? If she really did just keep on truckin' that long, is it realistic that she could be on chemo after all those years? One of my ideas for the story has to do w/ her wearing a wig, so I need to know if anyone can be diagnosed that long before getting chemo.What type of cancer would allow her to live that long w/o dying?Since she is up for adoption, because she has cancer would she be kept in a hospital or a regular adoption facility?
If your character has acute lymphocytic leukemia she could in theory have gone thru cancer treatment as a baby and went into remission only to have the cancer reappear as a teenager. It wouldn't be realistic for her parents to put her up for adoption because they couldn't afford the treatment. but it would be possible that they were in a social situation that forced the child protection agency to have her removed from their unsafe home and put into foster care (maybe her parents were drug users or in jail for a crime). Because of their drug use, the parents would forget to give her the medicine or forget to take her to the clinic for treatments. This would cause her to not go into remission until she was put into foster care. Then her parents would realize that they could never provide what she needed and eventually allow the foster parents to adopt her.The years pass and she is adopted and has not seen her parents for years.Then in spite of a long remission she gets sick again when she is a teen. So she has chemo again and loses her hair.Hows that?