I think you're on the right track for now. Hopefully the food switch will work
Soaking her raw paw in epsom salt is a great idea and will definitely help - you can usually pick it up at any drug store if you don't already have some - great thing to always keep in your medicine cabinet too
Alergies are tricky sometimes, but other times it's pretty easy to figure out the cause. Just keep working with your vet.
Good luck