The problem is the Supreme Court has said in terms of discrimination, transwomen are men. In terms of sex discrimination they are no different to any other man.
You're generally not allowed to discriminate on the basis of sex. But the law understands that sometimes it's necessary. Like prisons, sports, etc.
So they allow exceptions to the rule.
Which means you can have a woman only event, that doesn't include any men - in other words it's sometimes okay to discriminate against men on the basis of their sex.
What you can't do is discriminate against men and say you're not allowed here...except some men are.
If it's women only, that's it. No men. If you want transwomen in, you have to let all men in, otherwise they can say they are being discriminated against.