A.M.
I would take her to a Naturpath and some one who does viseral and craniosacral work. Also a chiropractor. I have not dealt with the arthritis in a child, but I do know many people can cure it ( I did ) with identifying what foods bother the person and removing them. When a child is having foods that they do not do well with the getting sick is one symptom and another is inflamation ( arthritis and other related things) It might be as simple as identifying her food sensitivities and removing those foods.
The body work and chiropractic will help the organs work better and help with nerve interference that might be causing some of the issue.