Suspected chicken allergy, advice? (Rash in second photo)

My pup is a little over a year old. She has had some redness on her tummy on and off for a while now. Our vet originally said it was fungal so we used the treatment they gave us and didn’t notice much of a change. We recently noticed it getting worse since we started using a chicken based topper on her food. So now I’m thinking it’s an allergy. We are taking her into the vet on Tuesday. But in the meantime, I wanted to start searching for chicken free food. Any suggestions? Her puppy food is a large breed puppy lamb and rice food, but it has some chicken in the ingredients. So I’m open to any advice or ideas!