Food allergy. Help with switching/testing.

Our dog has what I can only describe as being a food allergy. The vets have been telling us it's fleas, I don't buy it. Flea allergy often comes with food allergies, but there's not even a way for them to test for food allergies, and they are completely ruling it out, telling us to feed some low-grade food instead, which made her worse.
She's been throwing up a lot lately, and I'm at a loss as to what I should do. Technically, I just live here, and she belongs to my fiance's mother, who refuses to listen to what I say.

Either way, I intend to switch the food myself, even if it means throwing out the entire current batch. My question is what food should I start off with? She currently (and very unfortunately) feeds them dry food (a brand lower on the scale than Ol Roy, but this current bag is Purina) mixed with Alpo. The dogs both have horrid teeth. I advised against this, without any luck.
They won't eat dry food unless it's mixed with wet food, and even then, the smaller dog eats around the dry food.

I just am hitting dead ends here.

Well, to rule out environmental allergies, a blood test should be done.

In order to rule out food allergies, you have to do an elimination diet. Start with a single protein source food that the dog has never had before and try that for 3 months. Then you can slowly add in other proteins to gauge the reactions.

I recommend Mordy at www.betterdogcare.com. She's working on an elimination diet for Buddy as his allergies have gotten much worse.

Good luck.

Thanks BP.
They've done other allergy tests on her, but they keep going back to fleas. She has open sores on her back (which is missing hair) so even the vet is apprehensive about putting chemicals on her. I've been using the garlic and lemon treatments lately, and it has helped considerably with fleas.

I have been researching the food allergy symptoms a lot lately. The foot and mouth itching stood out the most to me. She is constantly biting her feet, and pushing her paws into her muzzle, which has caused her gums to swell.

Hopefully this will help her. She might not be my dog, but she still deserves a better life than this.

It's great of you to help, Raven.