Is it because she's made herself look like a ridiculous sexualised version of what they think a woman should look like? Well that's their own fault.
You must be joking, right?
She simply looks like any number of young women around today. If you don't get out much I assure you, she does.
I assume they all dress themselves in the morning; do you think any harm that comes to them on account of how they present themselves is their "fault" too?
I can't believe it's such a taxing thing to imagine why she might be more at risk in the men's than any other woman. It's trans/homophobia, folks. Has no-one ever noticed the angry reaction of men "tricked" into fancying women who are "really men"? Well let me tell you, it's real. And it makes some men furious!
If you're a woman in the men's, the guys might very well do what it seems many women here would do - say, "alright love, reckon you're in the wrong room, get yourself off to the ladies". If the response is, "no, I'm definitely meant to be here"... well you'd better hope they're not only not a sex offender, but also not a homophobe or transphobe either.
Now I don't think trans women are necessarily safer in the ladies these days, because apparently trans women make some women just as angry as they do some men these days (there's a name for that). Presumably they use the women's simply because they are women. If not to you, they are to them.