Hello & welcome,
I moved your message from the RSI sub forum to the TOS form, just to be sure you got more replies for your daughter.

Was it competitive swimming, with lots of training time?
The drs didn't suggest stopping the violin also?
At least until symptoms & pain get controlled ,and after full recovery from surgery if that does happen.

Since she is young she might bounce back quickly, but then again, I'm sure neither of you want take a risk of any long term chronic issues.

It might even be a good idea for her to consider some alternative hobbies and activities that aren't repetitious like swimming & violin are.
The static postures of holding the violin & playing repetitively is like a double whammy.

Please be sure to find a very highly rated surgeon & one that has done many of these.
Be sure to get second opinions.
Has there been any other testing to better pin point where the compression is vs just doing the surgery & hoping that fixes the problem??

Has she had any expert & advanced PT to see if that helps?

And has there been a MRI to check for any extra cervical rib or other anomalies?

some of our sticky thread with good info
Drs & PTs lists -
http://neurotalk.psychcentral.com/thread135.html
useful info-
http://neurotalk.psychcentral.com/thread84.html

It probably wouldn't hurt her to try the corpse pose from yoga.
Is her heard forward of her body , posture wise? same with shoulders , rolled forward or hunched??

If so, working on getting those relaxed and back into alignment with the rest of the body might allow more room in the areas that tend to get compressed & crowded.

Some do have anomalies from the norm, sometimes more detailed testing & imaging will show it , but sometimes it is only found in surgery.