I think your Head is more of a nutter than my ex-Head - and that's saying something!!! Ring your union at regional level. If you get the brush off, go higher. I think there are a number of us on here with experience of getting unions to act higher up the food chain. Make it quite clear that you are the victim of a series of malicious allegations and threats and that others in the school are too. Tell them that you have another job from Easter but that this woman's behaviour is making you very ill. Ask for their support in writing the grievance and taking further action against this woman. As OGW said, further up, it's what you pay your subs for. Tell them if they do not take your situation seriously, you will make a formal complaint about the union to the TUC.