The test is: 1 tsp of baking soda in 8 oz of water, drink it first thing in the morning before eating or drinking anything. If your stomach acid is adequate, you should burp within 5 minutes. Another way to test is when she feels heartburn, take 1 Tbsp. of apple cider vinegar mixed with water, or 1/4 tsp. of baking soda mixed with water. The vinegar will help if she has too little stomach acid, and the baking soda will help if she has too much stomach acid. Personally I'd try the vinegar first in this case as low stomach acid is much more common than too much stomach acid. If that makes it worse, then she can try baking soda to neutralize the stomach acid. Or she can just do the baking soda test first.
If she has too little stomach acid, she can take Betaine HCL capsules/tablets with meals. Eventually her stomach should figure it out and start producing enough stomach acid and then she won't need the supplement. I don't know how to treat high stomach acid.