I agree with Lovetodream88.....food allergies are not as common as environmental. Most vets do not start with food....that is a royal pain to do...and in the end, it is usually environmental. You can do blood work to see what she is allergic to, but I would only do that if I were planning on doing the injections to desensitize.
I don't do the testing any more. I have two pups with allergies right now...one of mine and a foster. They both have had injections of Cytopoint....it is a new med and is getting rave reviews. It does not have the side effects that many of the allergy treatments have.
This link below explains the percentage of food allergies in dogs. It also discusses symptoms of food allergies...and it discusses food trials. They are a pain in my opinion and if the poor thing is itching while you are trying different foods it is a pain for them...they have to be on the various foods for 12 weeks! Given the small percentage of 10% there is no way I would do it.
Food Allergies & Food Intolerance in Dogs