I also take a smooth muscle relaxant that helps the constipation (Cialis, in my case,
for its dual function) and Alpha Lipoic acid, which has aided my
peripheral neuropathy, and may aid the autonomic neuropathy as well.
If you mother has primarily diarrhea, then other treatments may be appropriate for her, but there should be a method to stop this problem once the root cause is known. Foods with laxative effects (like Sorbitol), overgrowth of intestinal bacteria, etc. should be ruled out.