Hi WTBH. I think your supervisor may be on a path to her own destruction. Her Superintendent is already aware of the way she's behaving, and the more extreme she gets the better for you. Don't assume you're the only one either, because if she's doing it to you, she'll have done it to others.
I am in a similar position to you (but a lot less extreme) , and I use the mantra that I can't control other people's behaviour, I can only control my reaction to it, as a shield against all the digs and unfairness. And her behaviour is being noticed by others and is not reflecting well on her.
Keep your cool and your nerve, go on acting professionally and don't assume others are on her side.
Looking forward to hearing how you go. I'm cheering for you.