Why is she doing it?

For the past three years I liked someone and I think he liked me too. Things did not work out because I was too shy to make a move and when he tried to talk to me I immediately acted like I had no feelings for him and he was just like everybody else. Half a year now he is in a relationship and I am doing my best to move on. The problem is that his girlfriend has started acting really weird lately. At first I noticed her staring at me during lectures but when I see her, she acts like nothing is going on. Now she has started copying my moves and style. What do you think is going on? Is there any reason she acts this way, even though I don’t make any moves towards her boyfriend?