Has she been checked for food allergies? Have you tried feeding her food you make yourself? It's not always additives that cause an allergic reaction, for example, I am allergic to beef, and celery (and a myriad of other things) - it doesn't matter how organically it is produced, it is the substance itself that will make me sick.

I'd speak with your vet about the possibility of it being caused by allergies, and what he could reccomend as a starting diet, whether it be trying simple steamed fish for a week, and seeing if anything changes, or what the vet reccomends.

Poor sweet baby, how old is she?

I never had food allergies until ten years ago, and have developed a broad spectrum of them since then. It can happen to anyone at any time in their life, according to the doctors I have asked. My skin doesn't react, but two of my siblings used to get excema in response to food allergies.