Your mother needs to be seen by a doctor asap as it could be an ulcer, gallbladder problems,a hernia, acid reflux, malabsorbtion, a number of things which need investigating properly by a doctor.
In the meantime make sure she avoids over the counter anti-inflammatories (she shold not stop any prescription meds without discussing with her doctor first) as they can aggravate conditions like ulcers.
Other things to be avoided would be alcohol, spicy foods, fatty foods etc...