TOS can be on both sides , or one, or worse on one than the other, depending on the cause.
I'm assuming her positioning placed the compressions on both sides fairly equally..

There may be nothing causative that shows up on her imaging, soft tissue & impingement's often don't, at least when it comes to TOS, unless there is some bony anomaly. But it would be good to have some other surgeons look them over in case something was missed.

Have you searched the web for any other stories of extremely long surgeries causing problems like this??

It might be helpful to email some surgeons ( usually you can do that from their websites) that do similar surgeries and ask them if this does happen and how long might it take to resolve?
That is what I would do, you need some professional opinions to find out if this is normal or rare & maybe a time frame for improvement.