The point is that you have not demonstrated that there is a legitimate fear of being assaulted by transgender women in public bathrooms.
However there is a legitimate fear of transgender women being assaulted by men. Have you ever considered tying to understand that?
See post #455, which strongly implies that your ally agrees that 7.5 million women will be assaulted in public places.
I do understand the point you make about trans women. But society largely runs in a utilitarian manner - as I believe it should - and your point is extremely weak from a utilitarian perspective. This is NOT to say we should ignore the fears of trans women. But we should NOT make all women less secure in order to help the tiny number of trans women you're discussing.
We need to constrain ourselves to considering only those solutions that help trans women without further endangering women.