It's the lesson we all need to have repeated for us from time to time: You cannot control another human being, you can only control yourself. Don't worry so much about your ex and what she might be saying or thinking, because there's really nothing anyone else can do about it.
I too have worried incessantly -- particularly prior to the custody hearing -- about what my xW has been saying to neighbors, friends, our S's teachers and caregivers about me. The best we can hope for is that we get our chance some day to set the record straight, otherwise what can be done?
The comforting thought is that God does know the truth, whatever false witness someone brings against us.
That's not to say it still doesn't hurt to have our character and the character of our M/R slandered. Or to hear the truth gutted and shredded by people we once trusted upon the altar of self-deception and self-interest. And it takes a lot more patience and humility to not respond in kind than I would have imagined as well.
Still, we're supposed to learn to not let that get us down. It's a road, a long road...