Why does my girlfriend like rough ?

My girlfriend is a feminist for women's rights outside the bedroom, TOTALLY submissive and subservient inside. She wants me to take control and "ravage her". Go rough , , f***, and say dirty things to her while we have . Pulling hair etc. Why does she completely opposite in the bedroom? She keeps saying things like "Mmmm put that big thing in me and rip my p..... up and dirty dirty stuff like that. I mean I'm not going to say no, but I'm curious as to why she likes it. Because to be honest, I love it when she dominates me instead. I think its y if she uses me as a form to get off but she actually wants me to like chain her up, hold her hands and go rough like that. Can someone explain? A girl perhaps?