There are two articles in the YT Library explaining puppy growth stages... here's a link:
Puppy Care and Puppy Info Library - YorkieTalk.com Forums - Yorkshire Terrier Community
Sometimes behaviors are just stages they are going through. Yorkies removed from the litter sooner than 12 weeks of age can develope bite inhibition issues. Bite inhibition is naturally learned from the dam and any littermates. If your puppy didn't learn this bite inhibition, you will have to teach her, and the best way for her to learn it is if you can mimic the responses that she would have elicited from her birth Mom or her littermates when playing/biting too rough or inappropriately.