I don't know if this will help or not. I was recently diagnosed (at age 44) with hypermobility syndrome, the ligaments allowing the joints to move past their correct stopping points. I have always been super flexible and always in some sort of pain, getting worse as I get older. I would suggest seeing if your daughter can get an appointment with a rheumatologist, an arthritis specialist. No, the condition is not arthritis, but this specialist was the only person to give me a diagnosis that actually fit all the symptoms after decades of questions. The recommendation is strengthen, strengthen, strengthen the muscles to help hold everything in place. Your daughter seems to be on the right track with swimming and dancing but I would personally question whether ballet is a good choice as you seem to stretch in the different poses and I was told that stretching is a no-no. (thank you to all the doctors and physios who had me do extra stretches all those years and probably made things worse.). Then again, I am no doctor and don't know exactly what parts of the body are involved in ballet.

I hope this may help. Www.Hypermobility.Org gave me more info after the diagnosis which further confirmed it. May be a starting point?

Good luck.