Maybe switch to bland diet and see if it clears up....if not doing it already give Beneryl 1 mg per pound
I agree give her some benadryl to help and I would make an appointment with the vet to have it looked at again.. maybe do a skin scraping? don't worry you will get to the source.. just have to figure out what is aggravating it but I would give the benadryl in the meantime.