Has your vet checked her blood sugar? Usually yeast needs sugar to grow and that can often be a sign of a sugar problem (in people and pets). Antibiotics can make the yeast problem worst. Ask your vet for "FortaFlora" or try giving her some plain yogurt (or acidophilus if she will take it) - she needs to replace the "good" flora in her digestive tract that the antibiotics have destroyed so she can combat the yeast.
bebo makes a great point: food allergies are often the root cause of chronic yeast overgrowth problems. You could also try probiotic digestive enzymes either from the pet store or the human herbal aisle at the grocery store. Acidopholus is a great first-line defense against yeast of any kind in the body, and is the same helpful ingredient found in active cultured yogurt like DanActive.
Another great topical remedy to try with the feet is Dermachlor Flush Plus. I had a dog who got doggy athlete's foot (yeast infection) every time I turned around - usually in the summer when she was swimming a lot and had wet feet. I just squirted the Dermachlor in between her toes and rubbed it in quickly for a day or two, and that was all she needed. Dermachlor is just a mild antibiotic, anti-fungal wash that is inexpensive and also prevents dogs from licking the affected area. You could use it on any infection, wound, fungus, whatever, and it's perfectly safe. I've only found it at my vet's office though.
You'll have to follow strict dietary rules to nail down a possible food allergy. It's not easy because you can't cheat at all with extra treats. You could ask for a referral to a dermatology/ allergy specialst, but it's likely that the first recommendation would be a novel protein diet where you start with chicken only for a couple of weeks, and then add in various grains like rice or barley and see if the condition gets better or worsens. Corn is usually a big problem in dogs with skin issues, so at least purchase a food that doesn't contain corn to start.
I have a friend whose golden retriever suffered year round with yeast infections... ears and skin. She tried multiple medications... frequent bathing you name it and she tried it. Then a groomer recommended trying the brand dog food innova. After all this time ( 5years) and lotsa dollars it turns out changing to this particular food did the trick. It sure can't hurt to try :-)