My son has JRA and I don't think this sounds like it. JRA is not fluid in the knee, it's where the immune system attacks the joints. His joints will get inflamed but not with fluid. He also never got a fever with his symptoms. How we found out is that he started limping and after many x-rays and a bone scan and no one could find anything, we were sent to a bigger hospital. The doctor there had us do an MRI and said there was so much inflammation around his ankle that he couldn't bend it, causing the limping. Blood tests can show whether she has arthritis or not, and I'm assuming they probably have already done those. Hope this helps and that you find out what is wrong! My son was diagnosed right before he turned 2, and we've had a few years to adapt, but with meds he can do everything the other kids can! Good luck!