I would ask your vet to do a skin scraping immediately - check for yeast right off the bat. Has she recently been in contact w/ any puppies? If yes, you need to consider mange also. Mites often go undiagnosed, but I'm not sure it sounds like this - but a vet could also help rule that out. Lastly, go the very bottom of this page until you see the Google search bar - search for Pyoderma on THIS SITE only - and read about it, see if it sounds like that at all.
Like others have said, I'd switch foods asap as acquired allergies are not uncommon - esp. when a dog has been fed the same thing for an extended period. This terrible allergy season may have been the trigger that unleashed reactions to both food and environment - but who knows at this point?
I'd just take action asap as allergies compound. Hope she finds relief soon.
