My dad did something similar to my mom while they were divorcing, it got bad, but as time went on things settled. They are now on talking terms, but it took for the divorce to come through for things to wind down.
I want her to get better, I don’t even want to be in her life anymore
That needs to come from her. There is only so much we can do, more and it indeed starts becoming obtrusive if that goes against her wishes, however dysfunctional they are.
She is now dating my ex, but she’s telling people I never date him. She’s clearly using him to hurt me cuz he’s not her type at all. She’s making me seem as a crazy person. I’m feeling like crap
As you fall off her radar, things will probably ease down. She'll find someone else to focus her energy towards.
If your ex comments on the situation, take it easy, he too will soon find out what she's doing, or it will happen to him as well. If you're still close to him you can be a friend, but beyond that, probably better for your own sake to stand back and watch the fireworks from a distance.
What happened that she stopped talking to you? 12yrs is a long time as a friend. Has she broken contact like this before?