So, the vet put her on Purina a year ago and she is now still on it? So, basically - the vet caused her yeast then? Argh! Just so you clearly understand what the vet is
really saying.....yeast infections that are triggered by "allergies" are from
food allergies. So, these aren't from, say, "generalized" allergies or environmental stuff - the chances of that are pretty much nil.
What I'm getting it is: Purina is a crappy food and I feel really bad for you and your pup bc the vet --> 1) shouldn't sell that crap in the first place and 2) it's ostensibly
through his care that she is now in the state she is in.
If it were me, I would get her off of that food immediately - and I would do a "hard switch" (meaning, NOT gradual); you don't have to do a hard switch - but given her state, I would risk the digestive stress and just do it. Get her on either a premium kibble/canned (it is preferable to add canned to kibble bc of better nutritional value and added moisture) or homecooked food.
Good kibbles: Natures Variety Instinct, Orijen 6-Fish, Wellness, Evangers, Canidae. There are others too - EllieMay's mom will have suggestions.
Also - I'd suggest you get her on active cultures (like in yogurt) for awhile. Are you near a whole foods? You'd want to buy some that is KEPT refridgerated or it is probably already dead (unless it is processed in more pricey way). Here is one you can get online, I trust its potency as well:
http://www.askariel.com/product_deta...emid=probiotic.
I really do want to help, so please keep us posted. The reason I'm so concerned is the extent of the infection. Oftentimes, yeast goes undiagnosed bc it just "lurks" under the surface. Your poor baby's infection (luckily) became obvious enough that you knew it had to be treated - so on one hand, it's good bc you can tackle it; on the other hand, it's a pretty nasty infection - but I want you to know there are people other than your vet to support you (and, maybe better vets out there too).
Take care, Ann