It's an interesting question - and one I don't have a simple answer for. Ultimately, any organisation can include or exclude certain people on certain grounds using a code of conduct - so the judge was probably correct in his legal positioning and correct not to get dragged into the morality of it. Do I think it's unfair that you need to wear special shoes or special trousers to go and play golf, sure. Do I think it's unfair that that there are certain clubs that won't let you without the right type of shoes... yeah. Can I change that? Not really. Unless the code of conduct violates a legal discrimination act - there's not much I can do. Had she been excluded for being black, or for being Jewish, or even for being a lesbian - here in the UK she would've had legal recourse to challenge.
However, on this occasion, the school is using an argument that there are certain things that might prohibit someone from being around their children in a position of trust. Pornography, like drinking alcohol, or taking recreational drugs, is something society attempts to keep 'adults only'. This is a moral judgement; but it seems reasonable. If someone were to show up and say 'I'm a high functioning alcoholic so I'm going to show up intoxicated' the code of conduct would likely exclude them. Same with smoking drugs. If you are currently engaged in the activity which precludes you from being around children - I think that is a fair moral judgement for a school to make.
If Ms Triece came to school and said I USED TO DO Onlyfans, but now I don't.... that is a different matter. That would be the same as someone coming to volunteer after rehab... but that's not the argument here. I disagree with your premise that there is a correlation between 'does adult content' and 'shouldn't be inside a school' - the correlation comes with 'adult content' and schools being a place of learning. She isn't banned from the school, her kids can go there, she isn't being given an endorsement and placed into a position of trust.
Long story short, I think the judge was right on this one.
