Are the drs sure there is no RSD/CRPS involvement with the ongoing pain? It's a nasty chronic painful condition that can sometimes happen from a slight bump to surgery.

The art focus should be fine, as she can come and go, take breaks with most art projects.
Guitar, not so sure, because of the postures, gripping, and repetitions... might be too much stress on the involved areas.

Is her pain level 3s-7s even with the meds? Is she on all of those meds at the same time, or tried them at various points in time?

Definitely go with the most experienced & skilled surgeon that you can get if you decide to go that route, to stack the odds for best results.

There is a possibility of adhesive scar tissues that might build up in the areas of surgery later on, some people may produce more of this than the norm. It is just something to be aware of as some surgeon don't mention this.

Poor posture really does add to overall TOS pain & discomfort, so have her keep aware of slouching - it closes down the whole area pinching things shut.

I don't know what kind of things they had her doing at PT,
were they doing "hands on" work for her (passive on her part) like massage, trigger point, ultrasound, heat, IF stim, low level laser, top rib mobilization, etc) ?

Or having her do active therapies like weights, pulleys, hand bike, stretchy bands? not good if pain levels are 3+ and esp. if pain increases, that PT plan is not correct for the client, needs to be re evaluated/readjusted.

Can she do the yoga style corpse pose comfortably?
That is a good place to start many x's a day, for relaxing and with deep belly breathing. Just hang out that way as often as she can as long as there is no increase in pain.
If she can do that well then the pictures on this link might be the next step to try-
http://neurotalk.psychcentral.com/album.php?albumid=422

I was amazed by all the positive help my skilled chiropractor was for me, he also used many of the PT modalities so covered that aspect in one shot.
Plus the added adjustment as needed, wrist, elbows, shoulders, hips, c spine, top rib...

There are lots of self help tips and things to help reduce pain & symptoms if myofascial causes, they usually won't work as well if a nerve is clearly involved.