Sounds like playing. Max growled playfully when he was a pup. He growled and grunted a lot when we played fetch and tug-o'-war. I think growling is a Yorkie puppy thing.
When he was unhappy with something, usually when I would accidentally bump into him, he would take my hand and gently put his teeth on my finger. He grew out of that.
The gentleness with the teeth that your girl is displaying indicates good "bite inhibition." As long as she isn't biting down hard, I don't think you need to worry.
Work on basic trick training and obedience, but I don't think you need to worry.
__________________ Kristin, Max and Teddy  |