@slayer - I have been in your shoes, although different topics and circumstances. It flippin' hurts so much at the time, and for some time afterwards.
Please don't do anything rash. Give this a little while to see how it plays out.
In all likelihood, the lady concerned will deny the conversation(, but of course you and she know it happened). Please document what transpired, because in a highly emotionally charged period our memories can start to fail us, over time and you may need cumulative evidence if this moves forward into something formal.
Moving forward document dates and times of anything that happens.
I must admit that I decided very early on in the process that I would not resign, unless I had been offered a contingency agreement, with a compensatory payment sufficient that I wouldn't have to work any longer.
Just to comment on the opportunity you initially discussed with her. I'd apply for it, because now that your position is clear, HR will ensure the recruitment process is followed to the letter and is fair - just in case this were to go any further.
In large organisations, and I imagine teaching will be similar, interviews run from exactly the same set of questions for every candidate, with answers recorded, then scored and those scores are compared during the decision making process. Each member of the interview panel will be doing that scoring.
I would go for it because you are cast-iron to be given an interview, and if you did end up moving on the interview experience would be good to have under your belt; especially if you've been in post for a while.
It's a rubbish time for you, but as I say, don't do anything too rash. Good luck with it all.