Welcome to YT! Just a little bit of info you will probably hear alot here ....there is no such thing as a "teacup" yorkie. A yorkie is a yorkie no matter what the size
. For training it takes a lot of patience just hang in there and give her lots of love I am sure you will be fine.
The snapping at your other dog is the puppy in her, your other dog will soon enough put her in her place lol.