I'm sorry for what you are going through fml. It truly does sound hellish.
As for the lawsuit, eventually it must end? She files, you respond, is there a court date set? Between filing and the court date I guess you are trying to come to some agreement with her to avoid court?
My take on this would be let it go. Stop all contact with her. She is obviously not participating in good faith if she is getting information from your STBXH to use against you, she is just playing a game.
Eventually it will go to court and if you are in the right (which I am guessing you are) things will be decided as they should be. Plus if you leave her alone and don't play, she might get bored and just settle.
In the meantime, stay well on your side of the street, perhaps go completely NC except where you absolutely have to with regard to visitation (and then perhaps only in email?).
I really think you need to extricate yourself from this right now, even temporarily.
Anyway, just my 2 cents.