I second the go-see-a-doctor suggestion. Its worth it in the long run.
I had carpal tunnel symptoms set into both hands in my early 30s, and struggled with it for a couple years. It shares a lot of the same symptoms and early treatments as tendinitis. By the time I finally got it checked out, mine had progressed beyond the preventative treatments. The naproxen, cortisone shots in the hands, and wearing wrist braces while sleeping all helped to some extent, but it finally took surgery to nip it in the bud.
I guess that one good thing to come out of it for me was a unexpected love of short scale basses! Other than that, it pretty much sucked. Hope your friend gets better soon.