These dogs should have introduced in neutral territory, like a park so someplace that neither dog feels territorial about. The Yorkie naturally saw your dog as an intruder and feels fearful and insecure.
Also, two spayed bitches often will have a hard time getting along.
You need to start over with these dogs, and realize it can take months for them to learn to co-exist. Even when they finally do, never leave them alone together.
Here's a good article on making introductions go as smoothly as possible.
Introducing dogs