You have my utmost sympathy. You have been more than reasonable - you've gone well beyond the call of duty. If the school will never take action because they don't want to lose face, then I think that seals the deal. (It's astonishing the lengths people and organizations will go to save face. Such lengths are not to be underestimated.) Essentially it's a toxic school. It is an enormous shame, but that's how it is. In a way it's not just this one appalling person that's the problem - it's the fact that she has the support of the school. I know almost nothing about what legal action you might take (if any), but I agree that it's pure wishful thinking that one day she'll be found out, and get her comeuppance. Yes in a "just" world things like this wouldn't happen. In the real world they do. The guilty often go unpunished - it's a fact of life. The deputy head who you spoke to is now aware of your feelings, and has the chance to act, and change things, if he/she wants to. From what you've said though, it seems extremely unlikely. Perhaps give them till the end of this week to approach you with what they intend to do about it. If you don't hear anything, then I go along with what @sabrinakat and @Yoda- have advised, i.e. leave.