Just saw your posts and wanted to say how sorry I am to hear about your mum. How absolutely awful for your mum, yourself and the rest of your family.
I had a similar treatment to your mum. My breathing levels have never returned to their pre-treatment levels and the chemo definitely had an effect on it. . I think sometimes the medics don't mention too much the rare side effects, and some staff have seemed none the wiser (from my experience).
However, the point is they do happen, and very rarely the treatment can kill rather than the disease. You just never know if you are going to get the rare odds, so to speak.
My very best wishes to you and your family,