I would go back to RAW, grain/carb free. Add a digestive enzyme and keep low fat to start - fat is hardest to digest, they need fat so add raw organic cold pressed coconut oil. 1tsp/10 lbs of body weight. But start at 1/4 of that dose and work up over 2-3 weeks.
Also apply it to the skin, at least where she cannot lick it off.
Bovine Colostrum is a safe supplement to assist the immune system. Proper Nutrition makes one that has 40% immunoglobulin.
If you go back to RAW, use " baby calves" liver as the OM, this has the highest ratio of Zinc - an important trace mineral for skin, hair and immune health.
He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion. - Unknown