Why not enroll her in a puppy class like you did with your Akita? My Yorkie graduated from puppy class a few weeks ago, and I thought it was great. You seem pretty knowledgeable about training, but I knew nothing to start with and the class taught me a lot. Maybe the trainers there will have suggestions for how to make a shy dog be more outgoing.
I would not put my Yorkie on a tieout though. It won't stop wild animals or stray dogs from coming up to her, and a Yorkie is just a snack to animals like that.
