My Yorkshire Terrier bully!

Question
Hi, I have 2 dogs-a tiny Yorkshire Terrier bitch(16 months old) and a rather large male Shi Tzu. I was planning to breed from them but my little Yorky has other ideas! She is very controlling of the male despite him being bigger and stronger than her-he has become very submissive and quite scared of her. Many times she has presented herself to him and encourages him to mate with her, but when he tries she then turns and bites him!
When interacting with me she knows that she isn't the leader of the pact, and Idon't encourage her to be dominate-but she is definitely showing signs of trying to dominate the large male!
Apart from this there are no problems with my 2 little dogs-they are very well behaved and obedient.
Why is she behaving like this? Do i need to take them to see a professional?

Answer
DO NOT BREED THOSE DOGS FOR ANY REASON!!! One does NOT breed a tiny bitch to a much larger dog, you will end up with a dead bitch and/or puppies that die in utero!

Have the bitch spayed, have the dog neutered.  An intact bitch will always control an intact male, given normal temperaments.  No one with so little knowledge of dog behavior and anatomy should even consider breeding.  There's far more to it than just allowing a bitch to become pregnant, and if you match up these two, you will find yourself with a huge veterinary bill and possibly a dead dog.