You're on the right track. Manage it however you can and keep her out of the loop wherever you can.

That last line of your post about audacity is exactly what it is. Intentional. That's what makes it worse, when you realize they aren't stupid, they're mean.

You mentioned she insisted on paying that $100 back, that's what falls under the cycle I call good-boy-mode. They are so good and do the right thing, so the next thing looks unintentional. Feels unreal at times, but oh, it's a pattern.

Hang in there.