I think you're being a dick, and that she just wanted to cosplay as a cute girl, without particular second intention. Generalizing like that isn't the smoothest thing you could think of.

Then again, it's the internet. Even if we assume she is a pure butterfly, she should have noticed by now that most of us aren't, and it was to be expected

Or…now hear me out here human projection booth; maybe she just does not think it’s very classy for a complete stranger on the internet to openly message people just to to tell them that they beat it off while staring at pictures of them…
you know, common sense shit.