Do not engage. Repeat, do not engage!

And she will escalate her behaviors and the directions from which she comes at you. It won't magically stop anytime soon, even if you disengage emotionally, she will try to reel you back in.

Work it out on your own and don't let it come to a reactive point (that was the biggest mistake I made, letting him bait me into a reaction). They don't care if your reaction is good or bad, hurts them or you or the kids, they only care that they get the reaction. Because then they feel vindicated.

You mentioned how hard it will be once she starts appearing in public with other men. If she's an actual narc, expect that you will see her going places and doing things with them that she wouldn't do with or for you. That's classic narc stuff, lovebomb the new person while punishing the old. One classic story I've heard a few times is the narc spouse who refused the other children, then six months after the relationship ends they're posting all over social media about how they are having a baby with their new relationship, it's something they've wanted forever, and they are so excited and can't wait. You get the idea. It's all a game to them, don't take it personally.

Stay strong. Bite your tongue. Nothing good will come from any interaction.