Start making fun of them.
You probably know your ex too well and you know her vulnerabilities. Exploit them. Maybe her mom died, or some other stuff.
Sensible point tend to make people feel like shit. Try to make her feel bad for being BORN. If you need help, I can help you and scare her off.

And YES, it is harsh, but if you're desperate for revenge, do it. You'll feel much better. She deserves it, anyway.