She's trying so hard to ruin my relationship?

There is a girl, who is a, and likes me. She was a nice FRIEND to talk to at first but then she became weird wanting me to call her daddy after everything and believed if I didn't that I was "disobeying her" like I was her ldaughter or something. But the thing is when me and her first became friends I wasn't datign anyone. Now I am and she knows that but she still persist with this behavior of "call me daddy" and "you're the only girl i wanna eff with" and all of this. My boyfriend feels threatened thinking I'm going to leave him for her but it's not even like that. How do I explain that to him and explain to her that I'm not interested but will still be her friend?