My puppy is 75% silky terrier 25% yorkie and she has characteristics of both. Like the other post said, silkies are a bit bigger (8-10 lbs), their hair should be that silky texture but not as long as a yorkies (hence the name), the coloring is same as a yorkies, the body is longer so to have a more rectangular appearance vs. a squared look for the yorkie. A silky terrier is said to be cross of a yorkie and an australian sheperd so to have the look of a yorkie but a bit bigger/sturdier dog. Silkies do have a longer snout and their ears are more on top of their head.
My Isla has the longer snout, seems to be smaller (at almost 5 months she's probably 4 1/2 lbs), but seems to look more "foxish" than a yorkie.
However, like the previous post stated, each breed has different variations and looks. Sometimes I think mine looks more yorkie than other people's purebreeds. It all depends on the doggie.
Regardless, they are all beautiful no matter what and if the breeder said she was a full yorkie, then I'm sure she is!