First thing, do cut out the treats for a bit. My boy is grain sensitive (well, sensitive in general) and a commercial pig's ear will send him hauling butt to the backyard! The raw ones don't though. Stick to higher fiber treats for a bit, carrots, apples (with the skin, NO seeds!), things that are one ingredient, identifiable and natural. I wouldn't use chicken because of the reaction to the kirkland food. If you can get it, I like to buy a beef heart, hack it into little pieces, sprinkle it with garlic and cook/dehydrate it in the oven at 200 for a few hours. Not too rich, natural and stinks good!
As for the food, believe it or not, I have had great results with the Natural Balance Limited Ingredient diet Fish and Sweet Potato. As far as I know, petco and petsmart carry it, if not, try a smaller pet store in town. They could probably order some for you. That food is decently cheap. Not the best out there, but produces some nice results.
Also, buy some kefir from the dairy aisle, or maybe organic, and give a few tablespoons per meal. Try to find the plain, or use the vanilla. Sometimes overloading the gut with good bacteria can help the immune system focus on other places to keep baddies out.
If no result, it could be a grain sensitivity, seems fairly common. Taste of the Wild Fish does well in this case and is one of the least expensive grain free foods out there. Anyone that carries diamond should be able to get it. Try feed or farming stores. My boy did very well on this.
August and september are also horrible months for allergies, even noirmally non-allergic dogs can get super itchy. Giving the benadryl can help with this, or getting a steroid shot at the beginning of allergy season and keeping on top of it with benadryl. Try wiping feet and belly when she comes in the house from outside to lessen some of the gunk that will drive her nuts later. Don't forget the armpits!
Hope this helps!