One more thing:
Since your mom drinks soy milk - make sure that she drinks one that is not made with carrageenan. It is a natural thickener that is made from seaweed but has been linked to gastro intestinal problems and cancer in animals. Most soy milks contain this ingredient but Vitasoy, Soy Dream, 8th Continent, and Eden Soy do not. I switched brands just to be on the safe side. You can do a search on carrageenan on the internet if you want to look at some of the research.
Hope your mom finds some relief, IBS is no fun!