Yes, I agree with Cogito. It is unfair, but you need to let it go. There is no punishment awaiting her. Maybe she will push it too far with other people one day and end up completely alone. Maybe she won't. But you need to stop thinking about her.
I went NC with my mother 2.5 years ago. Truly, no contact. I tried to build a final bridge with her, despite some truly despicable behaviour, and she was so vile, just so vile I wanted to hit her (mocked me for some abuses I'd suffered as a child/teenager). I told my exH I couldn't speak with her ever again. He tried to build a bridge and she provoked a similarly strong response in him and told her not to contact "me or my family ever again".
Her behaviour contributed to the breakdown of our marriage. He had nightmares for months afterwards where he found himself taking revenge. And that was horrible for him. It was a very harrowing time. But it was only the curtain call in a life of nasty, spiteful, malicious, behaviour towards me. It's no exaggeration to say, "she ruined my life" whilst she was in it.
Anyway, I digress, it means that, for me, she has just ceased to exist. I'm assuming that if she died I'd find out because, I'm assuming, someone would tell me. But they might not. She could be dead now for all I know.
I know I sound angry in my post. But I'm not. I have a pain in my chest now from recalling how she made me feel, and I'm shaking, but that'll pass and it's only because I'm thinking about it for the purpose of this post. In 10 minutes she'll be dead to me again.
But if I carried that anger round with me all the time, I couldn't function. It would ruin everything for me. And now it's started to subside again, I can see how much better my life is without her in it and that is the point.
It's not about punishing her. It's about taking care of me and my children and living a good and happy life without her negative influence. That is what the ideal outcome is for you, too. Who gives a shit about her and what she's doing, eh? It's early days, but it will get better.