Based on her coloring and facial features, she looks like a pure Yorkie to me. The coat is hard to tell at such a young age, but we occasionally have litters that some puppies have excellent silk coats, and some puppies in the same litter have sparse "coarse" coats as puppies. The hair eventually grows in as they get older.
If you are interested in an AKC DNA test, you have to pay a $500 deposit to get the process started, then the AKC will perform the test and charge the entire cost to the party found to be in the wrong (either the breeder, if the DNA test comes out that the papers are wrong, or the buyer if the papers are right).