She looks like she is mostly Yorkie, I would say most. Is she AKC papered ? I personally think is looks like she has a little bit of Papillon in her, because of her ears & nose/snout. Lol. She is beautiful tho.
I think that one of her parents was maybe half Papillon half Yorkie, which would leave her 1/4 Papillon & 3/4 Yorkie. Because you said you met both parents & you would have known if one of the parents was a completley different breed. Of course no one can be for sure. & if the breeder said that she was purbreed Yorkie, maybe they didnt know if one of the parents was a mix. I dont know. No one can tell you positivley. But my personal opinion is that I think that one of her parents is a Papillon mix
If you dont know what a Papillon is I am giving you the link to some pictures of them on google.
papillon - Google Search