Have you taken her to the vet for blood tests to rule out any medical issues?
If so, and she is fine, then I would think that it would be an allergy problem. California Naturals (
www.naturapet.com) makes a good food for allergies. Acana (
www.championpetfoods.com - also make Orijen) has a salmon & potato formula that is good for allergies as well. Both products use the fewest ingredients.
If you want to stay with grain-free kibbles but lower protein there is Wellness CORE (
www.omhpet.com/wellness) or Go Natural NOW (
www.petcurean.com) is even lower.