It is during this time that the female shows interest in male dogs. She begins to look for potential mates. You will know that she has entered this stage when you see small yellow spotting around the house. She is no longer bleeding and some changes have occurred hormonally. Again, you will also see her pick up an interest in male dogs.
The final stage for Shih Tzus is the few months where this ends. Typically, this only happens twice a year. It is only during this time that you can breed them. If you bred her during this time, this is the stage where she will begin to show.