Itchy feet
 

Not a Yorkie but I used to have a powerpuff Chinese Crested who had the same symptoms. The vet determined that there weren't mites but we never could figure out exactly what it was. She chewed her feet constantly and it really wrecked her coat when I was trying to show her. We did several things which eventually resolved all her problems. The vet gave her several steroid injections over 2-3 months, I switched her food from Eukanuba to ProPlan (had the omega 3 & 6 oils added), gave a daily vitamin that contained both garlic and brewers yeast, and applied Frontline plus every 3 weeks. The only thing we could figure was that she had a horrible reaction to grass or a flea bite allergy (we live on a farm that had tons of stray cats when we moved in.) We did this for her for the rest of her life and it really worked. I think the combination of the Frontline to kill any fleas that got on her, the steroids to settle down any reactions and get on top of the problem, and the supplements with the omega oils to boost her immunity and make her coat and skin healthier really helped.
I hope you can get answers for your baby so she isn't so miserable. I would recommend adding the omega oils and the brewer's yeast/garlic to help her skin and coat. It certainly won't hurt to add to her diet. Good luck
Teresa

feet mites
 

Wow, this is really helpful! I just bought her a new food loaded with omega3s and I can definitely get brewers yeast and garlic supplements. Lately (the last 2 weeks) she's been licking her knees and thighs more than her feet. She is not scratching a lot. When I first took her to the (new) vet, she did do a scraping above her eye, not on her feet. Gave her cortisone shot and ivomectin. Since she seems pretty content most of the day, I am trying very hard not to obsess about it. I am so glad I have Yorkie Talk so I don't have to drive Doggy Daddy nuts!!!:p