Are you looking in grocery stores or pet stores for the food. Grocery stores usually only have the cheaper stuff.
Maggie came home with Royal Canin puppy and she wasn't too interested in it. I always wondered if she had bad associations with it mentally since the store (yes, sorry!) we got her at was feeding it to her and she seemed to be the low man on the totem pole in her little group. She seemed to hang back and be intimidated by her sister and the other pups she was with. She was so sweet when we took her out though and I HAD to rescue her so she wouldn't be traumatized any more.
Anyway, back to the food....I read on the Royal Canin bag or website that yorkies can be fussier with their food. I bought the Royal Canin YORKIE puppy (as opposed to the RC puppy (not specific to yorkie) food and she loved it! So, I believe maybe yorkies are fussy and that is why yours doesn't like her new food. Plus, it is too early to change it, really it is.
The RC site says this "
Fussy Appetite
We’ve created a diet with intense flavors and aromas to stimulate the Yorkshire Terrier puppy’s less developed sense of smell."