I think the problem is that she's kind of not wrong, it's just a social norms issue, and if the social attitude shifts, there will not be a way to enforce a rule that is not culturally supported. A lot of social norms have changed over the years including many to do with privacy and sex-shared spaces, so shared or partially shared bathrooms could just become the new norm, and I don't think laws would stop it from happening. It would just look outdated where they tried to hold it up until a judge changed the law. The difference between justice and social norms is not as wide as we might like to think.

So it's not that self-ID is changing everything, but that it's reflecting a change has taken root in some parts of the culture and affirming it as widespread and legitimate and the right way to think. It's not the law itself but our cultural response and conversation that really matters. If we say "well, we can't stop them" that misses the point. The question is, should they want to go into the women's loos to start with? What right as a TIM is someone being denied by having to use the men's private areas? Why do they need access to women's rooms? Usually there is a longer line for women's rooms especially since we have to sit for everything, plus approx 1/5 of the population may need to change a tampon, so why should they infringe? There's no argument for their need.

That doesn't mean no one ever broke the code in the past - but there was still an expected code, and people who were "going stealth" and getting around it were making their own choices. Now, they can just be open as trans, as most of them are and use the actually appropriate toilets. If they're somewhere that they're still not "out", they can make their own choice about trying to hide or not: as with every part of their life, they can try to live a lie that most people don't believe anyway, or they can come out and be proud - and acknowledge their real sex.