Sunny's possible fish allergy/intolerance

I'm still trying to find a food that Sunny can tolerate that is also high quality. She had no issues with the Hills Ideal Balance, but they've changed their formula so I don't know if it would still work or not. However, I wasn't happy feeding them that food because the protein level was lower than I liked and the fat was too high. Sunny SEEMS to be allergic/intolerant to fish (and it is pretty bad because even fish OIL causes issues if the fish is indeed the problem). So, now my next move is to eliminate fish products in the food and see if it helps. If it does, great! If not, I'm going to have to try something else. Another possibility is sweet potato in the food but I figure that is MUCH less likely because she had issues on the Chicken Soup brand and that food didn't have sweet potatoes (it DID have fish though) plus sweet potatoes are NOT a common allergen. So, even though the Blue Buffalo Wilderness Chicken Recipe is great for Smokey and is a great food overall, I can't stick with it. I'm going to try the Blue Buffalo Wilderness Weight Loss Formula because it has NO fish or fish oil (and the weight loss aspect will probably be good for Sunny, who still needs to lose weight). Canned food is even harder when you can't get something with fish because almost all canned foods have fish or fish oil (for flavoring and Omega 3) in them. There are a few Wellness foods that don't have fish (the Healthy Indulgence line pouches for SURE) and a few Blue Buffalo ones too. I'm sure there are others out there (if you know of any that are NOT Purina brand, leave a comment below please!) that I haven't found yet.