If the food is a low quality food or has grains, chances are her body has just finally had enough of the grains/poor quality. Pups are usually ok, it's once the get a little older that the allergies come out.
I suggest grain free food. Acana, Orijen, wellness CORE, Instinct (grain free) or if your budget doesn't allow for a more expensive quality food then try out Taste of the Wild, 4Health...both available at the tractor supply store.
"It's a nokalokapoopalotadoocanidragaleashalupus. It's a breed of mixed, strained money extorted
practically useless spin off of a once noble breed." --William Williamson