I'm sorry your mom is having a rough time of it right now. I don't personally have any experience with bone mets, but there are others here who will be able to offer good advice.
As for the anti-anxiety meds, you wouldn't think twice about taking an anti-biotic if you had an infection and you shouldn't think twice about taking meds to counter anxiety. It's a sign of strength, not weakness, to recognize when you need help with something. Remember, you're no good to your mom if you let the stress take over.
I'll be saying prayers for you and your mom.
Trish