It could be she has allergies to turkey (fowl) or potatoes or any one of the ingredients in the food. It could even be from the Iams if she was scratching at the breeders. All you can do is eliminate the source.
Can you try a unique food source like venison or rabbit? I believe it is 6 to 8 weeks for the allergen to completely leave the body.
Assumptions do nothing but make an ass out of u and me.
We can stick our heads in the sand for only so long before it starts choking us. Face it folks. The pet population is bad ALL OVER THE WORLD!