She definately looks like she has some Yorkie in her if not full Yorkie, but who can really say if she is "all Yorkie." Looks can be deceiving...there are often cross bred dogs that highly resemble one breed and possess little if any physical characteristics of other breeds that may be attributing to their genetic makeup. No way of knowing for sure, really.
In any case, she is adorable--that is what matters most! Congrats on the new addition.