Earlier quoted context omitted.
One way to possibly look at this is that she opened up to you because she felt you might understand, to her you responded sceptically and out of professional self-interest she downplayed the whole thing. That doesn’t mean those guys are necessarily creepers but that you’ve definitely lost her trust.
What would you suggest a proper response is... "yeah, I know!"? To me, asking "what do you mean?" is a perfectly valid response to someone openly name calling people you know.
You’re dealing with another person sharing something that is probably emotionally difficult for them to say. I’d suggest a subtler approach than immediately busting in with the evidence requests. It’s a slower process which is neither immediately believing or disbelieving the accusation but taking it seriously. Being open to the possibility and seeing where it leads rather than shutting things down because it’s uncomfortable. Because presumably the woman is also someone you know that you wouldn’t want to be hurt as well.