She definitely was in the wrong, 100% with that past guy. 

That said, according to you, she's now telling guys who approach her in that way to back off and handling it appropriately. Just look at Reddit, probably 70-80% (made up number) of people who comment here are men. Most of my female friends aren't really as into the whole "internet" thing as I am, so it makes sense that her internet friends would be primarily male. 

But that's another problem in itself too, she should have real life friends. Then again, what would happen if some of those friends are male? 

You have every reason to not trust her. But if you can't trust her, then the relationship needs to end.