Food allergies are rare, so I'd be wondering more about enviro / seasonal. Check pollen.com to track current pollens in your area, bc that may be what she's allergic too.
Allergies are tough. You can try OTC meds - most Vet Derms recommend Zyrtec or Claritin over Benadryl bc you only have to give those once a day, whereas Benadryl should really be given 3-4x day to be effective (it has a very short half life). See if the OTC meds work. If not, then you could move to Temaril-P or steroids, both which come from the vet. If allergies are all yr round or close to it, then you want to consider Atopica or allergy testing.
This is a thread about how to approach allergies:
http://www.yorkietalk.com/forums/die...tart-here.html