I was told by many people to avoid chicken for my food allergic pitbull as well. It turned out beef was in fact the problem. In fact he does not do well on any red meat. Could be the same for your pup and that is why she is reacting to the Fromm Gold Large Breed Puppy, as it has lamb in it. We also switched off NexGard for the same reason (the beef), as per the vet.
Large Breed Puppy formulas are designed with a growing LBP in mind. They will not cause your pup to gain weight unless you overfeed. It is a tired old myth to feed a LBP an adult maintenance food, though a lot of breeders, dog clubs, and vets still recommend it. You are absolutely making the right choice in keeping her on a large breed puppy food.
No self respecting vet will suggest an allergy blood panel as they are notorious for being inaccurate. The only way to properly diagnose a food allergy is by a food trial either with a homecooked diet of a single novel protein and carb or the hydrolyzed protein vet diet. That is what we did for our pitbull and he is doing excellent now on a fish based diet that is grain inclusive. He does terrible on grain free foods.
