Take her to the vet, they should be able to do some tests and figure out exactly what she's allergic to, and don't take the 'she's allergic to everything' answer... most vets tend to choose the easy way out and prescribe general treatments that leave the poor dog drugged all day.
I have a bichon frise that's 'allergic to everything' according to the vet, so I had him on prendisone and hypoallergenic food, until I took him to a real vet that did some skin tests and found he was allergic to chicken... and the hypoallergenic food happens to be based on chicken
