She should choose foods that are higher in omega-3 fats which are anti-inflammatory. If these don't cause any discomfort, she may enjoy foods like avocado, hemp seeds, olive oil, cold-pressed coconut oil.
Since she is in treatment, you will need to make sure that anything new with her diet is cleared by her Dr. to make sure there is nothing that interacts with medications or a certain protocol that he has suggested.
Check out more info here: http://umm.edu/health/medical/altmed/condition/gastritis
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