What ingredients are the same in both the Acana & the Orijen flavours you were using that is not in the Iams?
There must be something (other than quality
) that she's reacting to........ maybe it's a grain/wheat or a vegetable/fruit or some other vitamin/mineral additive - they're not necessarily always reacting to a protein
Nothing else has changed while you changed her food? ie new soap / new blanket / old soap but just washed her blanket etc