Another possible problem she might have is celiac disease. If someone has celiac disease, they need to avoid eating anything from wheat, barley, rye and oats. You can look the diet up on the computer - it is called a gluten-free diet. If this is her problem, her body will start healing if she stays away from these foods. I hope this helps.
It sounds very much like what my mum has, which is Crohns disease. The digestive system becomes inflammed as it detects food as a foreign body and builds up a defense against it. This is what cause the discomfort when she eats. If this hasn't been diagnosed yet, its best to get her admitted into hospital for tests just to confirm, or she will not get the treatment she needs.