When a cisgender woman and a transgender woman go into the same bathroom- just go use the same goddamn facilities, no other context necessary- the cis woman is not the one who has a right to feel threatened.
Even if they have been assaulted in the past. Even if they have every right to fear men.
You want to know why?
Because neither trans women nor men pretending to be women (I say to make painfully clear that even in this hypothetical situation they are COMPLETELY DIFFERENT GROUPS) assaulting cis women in restrooms happens enough to be even remotely statistically significant.
Because trans women by contrast experience a very real risk of violence every time they are forced to choose either a men’s or women’s restroom
BECAUSE TRANS WOMEN AREN’T MEN, ASSHOLES
And frankly, if anyone has the right to start screaming bloody murder when they see another woman in the women’s restroom? It’s trans women over cis women.
So hey, if you’re a cis woman, and you see someone you think may be a trans woman in the bathroom, do the world a favor-
Don’t be a jackass.
(Oh, and, while we’re at it, people with penises aren’t the only ones who assault cis women. Nor, obviously, are cis women the only ones who get assaulted.)