It only takes about a 1/2 cup to 1 cup of flax. A good coat elsewhere is a good sign that things are ok. Probably just an allergy. The only way to pinpoint is to take away every factor, allow her to heal and add them back in slowly one at a time till you find the trigger. Just fyi, some horses are allergic to grass O.O dust wood oils..things found in every barn. You will have to be very diligent to find the trigger but it would be worth it.