Welcome to Yorkie Talk. You will find a lot of information here on how to give some great care for your little one.
What is her name? As you read, there is no such thing as a "teacup", many times it is only a term used by some breeders to charge more for their Yorkies or refer to them as being extreamly tiny.
How old is your little girl? She is pretty small right now so it's important to keep her healthy. It's important she eats/drinks and not have any episodes of hypoglycemia. Also, she needs to stay warm, not be overly stressed/exersized, and needs plenty of naps.
Regarding her size, there is no guarantee. A 6-7 lb Yorkie is NOT huge by any means, it's within the standard and that's wonderful.
I hope you enjoy Yorkie Talk as much as we all do here!!