As her abdominal pain
is related to food,it can be due to Peptic ulcer
Give her drugs like Tetracycline
,Bismuth and Rabeprazole for H.Pylori .Add a Pre and probiotic capsule also.
If there is no response,get her investigated with Upper GI endoscopy and Ultrasound abdomen.
Give her high fiber diet
If you come back with above reports,i will clarify further
Wish her speedy recovery