Not much until they hit the showers, but better yet ask that individual what sanitary napkin they prefer along with what steps they will take to prevent from getting pregnant including using an abortion if those steps fail, along with all the other issues girls and women would have to face due to their biological makeup,
because growing your hair long shaving your legs and donning a dress will now allow you to gain that elusive insight into what a real girl/women has to go through their entire lives just as if you were one, just disregard the fact that they can still use a urinal like every other biological male without having to drop their pants.
I think you're somehow managing to stake out a more extreme position than TERFs, which is frankly kind of impressive. First off you're implicitly denying the existence of reassignment surgery, which in the case of transwomen matters a whole hell of a lot more than their Y chromosome when trying to use a urinal. So great job establishing that you have any idea whatsoever what trans people's lives are like. Better yet, you attempt to use knowledge of life experiences as a criteria for bathroom use in the same post where you demonstrate you have no idea on the subject.
Meanwhile in reality, we have (trans)women who look like women in every way outside the stall who want to use the women's room because unlike how them having different chromosomes and genitals that are different in construction if not appearance affects the bathroom going experience of people who aren't looking in their stalls (a gross violation of privacy), being a woman who looks like a woman can and has gotten trans women harassed, assaulted, and raped. I think by your standards, you aren't fit to use the same bathroom as trans women far more than they aren't fit to use the same as you.
Also you lead off by implying that post-menopausal women and women who've had hysterectomies aren't women either.
Good job!
If you want to say that trans women who can't pass should be discouraged from using the women's bathroom, that's one thing that you can make an argument for (I'd disagree but that's an actual discussion), but this is just a mess.
I brought it forward as a potential proposition, to sidestep the idiocy that is the federal government attempting to control at what 'stage' of 'sexhood' someone should be in slot a or b. You called it out as being untenable based on 'common sense' and 'because everyone knows this' without anything to back it up. So whatever, I guess every argument can be shot down with 'it's common sense, we don't even need to look into that'.
Going back to it again, would you have stated it was 'common sense' to leave bathrooms segregated, because nobody wanted whites and coloreds in the same restrooms?
The best solution would be a unisex handicapped bathroom so handicapped people, mixed gender child/parent pairs and trans people who don't feel comfortable trying to pass in one or both gendered room have an option. That requires infrastructure changes though.