I don't know, what planet you guys lived on. But in my world, until a few years back, female only spaces were occasionally speckled by creeps. It was rare, because women would raise hell if some creep paraded around their penis and may have called management if they suspected that someone was a actually man.
There may be some utopia where this never happens, and your daughter will definitely never see a penis, or male, in the changing room, for the mere reason that this is her right. But I've never been there. If you can tell me, how to achieve it, I am all ears.
Now, by contrast, and even more if self-ID becomes law (it is already applied in some places, not being law), a woman cannot object if some creep parades around their penis in a changing room, after all it may be a female penis and erections are something natural, aren't they? Not even a beard is enough to absolve a woman of bigotry and harrassement, if she calls management to have said person removed.
Personally I would go back to scenario a, or - if you can tell me how - to scenario b. Can you?
Now, if your point is, that males with SRS should be allowed in those female only spaces and no GRC process exists (is that your point?), I would like to point out that also in this scenario, you will not be able to police that, unless you change policies, so that women are empowered to call management and have the ID of any person they suspect of being male checked. Even if the law says it is clearly your right to have female only spaces and no male is allowed to enter.
It is a bit like the right to property. That stealing is outlawed doesn't always mean that nobody will steal from you. Therefore procedures were developed to hold thieves to account...