She's likely jealous. I have one that gets jealous easily, even with her "brother" who's been with us for more than 3 years. We foster occasionally and Uni is wondering when Toto will leave! (He's not.) Uni was with us first, so she prefers to be an only child, though she does play with other dogs, bc she knows they are not staying, or they are just friends she meets at the park.
I would suggest to give attention to the yorkie first. Greet her first, feed her first, etc. The puppy will learn the order. I'm sure the puppy will also learn quickly that he is bigger than her and play more softly, as many large dog/small dog households do, but you have to make sure she doesn't get too aggressive and piss him off bc one little swipe or bite and she can really get hurt.
__________________  The T.U.B. Pack! Toto, Uni, & Bindi
RIP Lord Scrappington Montgomery McLimpybottom aka El Lenguo the Handicapped Ninja 10-12-12 
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