A full recovery is also more likely for people who are younger and athletic. This was mentioned in a youtube vid interview of Julie Freischlag, and I've seen it anecdotally in articles covering people with TOS.

Nevertheless, she may have to choose at some point between swimming or orchestra if she doesn't get back to 100%.

She might also consider a routine of gentle stretches, breathing exercises, basic yoga, etc. to do before and after orchestra to help align, stretch and relax her body. My routine is around 25 mins and I do it every morning.

Good luck.