There is a medical condition called "ileus" which, basically, is a standstill of the intestines following their manipulation during surgery. I suiggest that your mother revisits the surgeon and asks for help - and specifically asks whether she is suffering from an ileus. If so, are there drugs that can be administered to re-start the peristalsis of the intestines and thus return to a normal nutrition cycle?
regards
Morecambe
It can take a while for everything to calm down. Do ensure she is not having too many loose stools and ending up dehydrated. Make sure she is at least supplementing with Boost or Ensure drinks. Make sure she is getting enough potassium, sodium and magnesium too.