It's quite true that you can't tell someone what is offensive to them, but that's entirely beside the point. If someone is offended by something and takes no action then that doesn't matter at all. But if someone does something in response to how they feel they were offended, we're going to judge that response by how reasonable that offense seems to us.
If the two men in the situation we're talking about had been making crude remarks directly to her and she had contacted the organizers I don't think any body (I care about) would have questioned her actions. If she had pulled a gun and shot them, then I think everybody would agree that that was unjustified. And if she had complained to the organizers because the men were wearing VI polo shirts and she was a diehard emacs user that would also be unjustified.
And there are some forms of receiving offense, such as when a racist seeing a black person at a Python convention, where them taking any action at all based on that offence would be wrong. I'm sure there was at least one person like that at PyCon, but I'm also sure that society has trained them to keep their mouth shut. And a good thing too.
So we don't get to tell Adria what is offensive to her, but when she shames someone based on that offence we will judge her shaming based on how valid we judge to offence to be. If one of the men had told her to her face that women didn't belong at PyCon then I think her actions would have been entirely justified. As it was, not so much.