My understanding (though I am a man, so grain of salt) is that women's nights are often not about only having women, but for having a time where the people feel safe, and that they aren't going to be preyed upon. Trans people have many of the same issues as women in this way, so it makes sense to include them. It should be a "statistically more likely to be assaulted than assault" night, but that name doesn't sound very good. I guess a "no men" night also works, but also doesn't sound good.