she said that all abusers had once been abused themselves.
At this point I stepped in to ask the question "but surely it's not the same in reverse- not all abused kids turn into abusers?"
She said that yes, all abused kids turn into abusers.
Its sad but many people have been taught to believe this myth. The truth is that SOME abusers were themselves abused. And that SOME abused kids grow to become abusers. But there is no generalization that can be made, nor is there any evidence to support this idea. From Psychology Today 1/30/2011 Talking About Sexually Abused Boys and the Men They Become
Many believe sexually abused boys almost inevitably become sexually abusive men. But, while a significant proportion of male abusers were victims themselves, there's evidence that relatively few sexually abused boys actually become abusers. Because of the myth, however, many men fear they'll become abusive or worry that if they disclose their history, others will consider them predators.
You might consider bringing this article to your friends attention, but you may have to explain why you're pursuing the subject. If you're not ready to disclose to her you may want to wait. Good luck.