I agree. Ear infections/scratching can be serious. Ellie was on Royal Canin for liver compromised dogs. It had corn in it and she scratched to the point of making her ears bleed. We took her off of that and I did not want to go with Science Diet L/D. I gave the vet permission to atleast see if there was corn in the L/D and said I would consider it. Thank God there is corn in it so we couldn't use it.
The only real choice at the time was to homecook or use vegetarian food. Ellie is fine now as long as she doesn't eat anything with corn at all.
What food was she on before that made her itch? Maybe you and your vet could try to find the exact allergen or she will be stuck on Science Diet forever.