Cat allergies

I'm hoping palmbob will see this and give me a little help. I have a five year old meezer girl, who suddenly developed an allergic reaction to something, this spring, and has had some cortisone shots and antibiotics to help with her itching and the subsequent skin irritations and infections. It comes on very suddenly, she will be fine for a while and then, BOOM, there it is again.

She is a very picky eater. She was a rescue and we didn't know what she had been raised on, tried several different foods and she would eat Iams, so that's what she had for a long time. A couple years ago, we switched all our meezers to Felidae, which they adapted to well. Except for her. She still wants Iams. Won't eat any of the little specialty cans of cat food. No snacks. None of them get treats. Now, we've had her on dry Natural Balance Duck and Peas, which she doesn't like much, but she will eat some. She's lost weight, and now I've added canned Venison and Peas, which she will condescend to eat if I add water to it and warm it up. (rolling eyes here) These foods contain no grain products at all.

Our vet suggested a specialist, but I'm not sure finding out that she's allergic to common things like household dust, other cats, humans, or grass pollen (although none of them go outdoors) is going to be much help. My cleaning products are nontoxic and haven't changed over the years, no new detergents or cleaners....I'm afraid if she stops eating the duck or venison she'll just starve. I'm more than willing to make food for her but she doesn't like table food, such as chicken or fish. I'm at a loss here. She's a sweet girl, loves to play and is very affectionate, it would break my heart to lose her. Help?