:lol: get a sense of humour bushy. I'm not a keyboard warrior, I don't get into fights and I don't pretend to be tough on a forum. I don't think you're a keyboard warrior either, I think you're a neanderthal.
You don't need to explain to us, we know it was wrong. If you don't care, leave it, but if you do care, then do something about it. I've given you one option. If you have it in writing (even if it's just you making notes during the conversation, which counts) that they'd have called the police...
That's ridiculous. Go and discuss it with whoever you've been discussing it with, make notes, talk about what would have happened if you had done it, write down their answer. Then go and see the head, explain that it's not acceptable and that you expect the school to write to the woman about it...
Really - how have they admitted that? Get it in writing, then make an official complaint, insisting that the other parent get a written warning about her behaviour or something. I don't see how they can justify nothing for her, but police for you.