She orgasm from the psychological stimulation of you dominating her by fukking her in the ass without her permission. That's why it turns her off if you ask.
She can't orgasm from vaginal intercourse because you stroke is trash and your not holding her down. I'm mean physically hold her down. Pull her hair, I'm mean seriously yank her head, call her a whore and tell her to cum for you. You're welcome. Use a safe word.

whew somebody said it lol yeah OP you need to figure ya ladies parts out. Prolly out here jackhammering her to glory x_x