My pup used to be horrible about the ankle biting. We've worked past it using an OFF! command that one of my friends who owns several big, rambunctious dogs suggested teaching.
Keep a lead on her while she is in the house for a while. When she bites an ankle, take up the lead and give a short little tug on it-- not enough to stress her or harm her (remember, these dogs have delicate tracheas, so don't correct in such a way that you're applying pressure to the front of her throat!), but enough to let her know it is a correction. I'm not even sure I can describe how light of a touch works to get the idea across-- it is a lot less than you'd think, and I think it is actually the jingling of the tags that startles her more than the lead itself. When she lets go of the ankle, tell her OFF! and then give her a treat or praise her. Eventually just the OFF without the lead correction should be enough to get her to let go of the ankle.
I'm really not sure how well that would work on teeny-tiny yorkies considering how delicate they are, but my girl is pretty big and sturdy, and it worked really well. She got past needing the lead correction in about two days, and now will OFF pretty reliably even when she is really riled up and wanting to eat my sock with my foot still inside. What's especially nice is that you can apply OFF to other things, like if the dog is jumping on somebody who comes to the door, or trying to do inappropriate things with somebody's leg... it's handy!
