I had a girlfriend for awhile who was, frankly, a bit crazy. A rather wild girl. But that wasn't all. She had a sister who was a whole lot crazier. My girlfriend claimed that her lunatic sister once forced one of my girlfriend's previous boyfriends to have sex with her (the sister) at knifepoint.

Having known the sister, I'd say it was definitely possible that that she might have done that. She was full of unreasoning anger and was looking for something all the time, but I doubt she had any idea what it was.

Such assaults by women on men are certainly rare, but they do happen now and then.