My girlfriend is a typical girl - sweet as anything, and our sex is fairly rough (choking, hair pulling, some degrading talk.)

But she recently told me she has a rape fantasy and I got mad at her and we had a fight. I couldn't understand why she wants me to pretend rape her. But I'm starting to get worried this is a core part of her sexuality (she watches master slave porn exclusively) so she's not gonna be satisfied sexually otherwise.

How do I even go about talking to her about this? Our only conversation I said I wasn't interested, but I'm considering texting her saying I've changed my mind. Anyone have any experience with this or any tips?