What can I do about my rat terrier puppy?

This week I gave my four month old rat terrier some steak for a treat. BAD IDEA..it made her sick with diarrhea. I got her back in December of 08 and I started her on Cesar with Science Diet hard food, then transitioned to Iams hard food. Well when she got sick I took her to a different vet because my vet didn't have a doctor in. So when I got there he asked what I feed her. I said Cesar with Iams hard food. I was deemed to be a bad doggy mom because according to the vet, Cesar is the worst food out on the market. But little Audrey LOVES it. He recommended science diet. Well I took back the Cesar and got Van Patterns Natural Balance eatables. She does not like it!! She got two shots yesterday and since then hasn't had an appetite. I bought some more cesar and she still won't eat. Her eye are watering, so the vet told me to give half a children's benadryl. I don't know what to do? Any suggestions.