Welcome to the forum. Xifaxin (rifaximin) is an antibiotic that works within the intestines to control the bacteria that produce ammonia. It is expensive, but it does help.
If your Mother is having extreme diarrhea, her doctor needs to be notified immediately. This is not normal. She could become dehydrated quickly. Lactulose is intended to produce 3-4 bowel movements a day, not extreme diarrhea.
I’m sorry she is having to suffer from the side effects of ESLD. Good luck to you and your Mother.