Hi Purist! I was on Omeprazole for years because of reflux due to too much stomach acid. My stomach eventually became very distended. A doctor told me "You're fat!", which was both insulting and unhelpful. After having read the leaflet in the packet and finding no solution, I went online and found "distended stomach" amongst the side-effects on an American site - so not just "fat!". I visited another doctor and told them my findings and they switched me to Lansoprazole. My stomach bulge went down gradually and I've been fine ever since.
I hope your mother is okay now. The only medication that gave my father a cough was Ramipril, for high blood pressure, but a Ramipril cough is very common. I got the same cough when it was prescribed for myself, but the side effect wore off in time and I don't cough any more.
Don't forget that most antacids are just flavoured chalk and can affect the colour and (how do I put this tastefully?), consistency of bowel movements. So don't be alarmed if this occurs!