Zio has seasonal allergies and we give him the generic version of benedryl: 25mg 2x daily. Otherwise he makes weird coughing/snorking noises & his eyes are red. Fortunately, after Summer is over & it gets cooler here, he doesn't have to take it.
How often & how much are you giving your dog? It might be worthwhile discussing dosage with your vet to see if you can safely up what you are currently giving her.
To be honest, it really sounds like she has seasonal allergies just like Zio has, so fiddling with her food isn't the answer.
Bonne chance,