Good morning all, I'm new to this wonderful site and also a new yorkie owner..(i think)

so my question is do i have a yorkie?? i got my new lil friend from a neice who could no longer care for lulu and said she was a yorkie, and since I am not familiar with this breed I thought maybe some of you yorkie lovers out there may know...(fingers crossed) she is 4.5 pounds and almost 2.5 years old. But everytime I take lulu out either to petsmart or the vet, the groomers and even to farmers markets everyone ask is she a yorkie mix?? AND I HONESTLY DO NOT KNOW as I thought she was a yorkie period...though I must say it doesnt really matter because she is a wonderfully loving and sweet lil thing...BUT I just kinda wanna know..

So I have posted some pics if anyone could take a peek that would be great..thanks so much, have a Wonderful day all....