When I was suffering as much or more from the treatment as from the infection, the ID doc was my salvation - after culture, he consulted by phone with National Jewish Health. Mayo, NJH, and a few other places are different - they are more willing to try the latest treatment models, and to treat the whole patient not just the lungs or infection.

In your place, I would try first to lean on the ID doc doing a phone consult with NJH about treatment choices for your Mom. (It might be easier on her than a winter trek to Mayo.) Failing that, it would sure be appropriate to seek another opinion.
How did the 2 of you feel about her ID doc?
Sue