The only way is to rehearse, rehearse, rehearse -- sit down and lay it out. What you are willing to talk about, what you're not willing to talk about. What you consider your business (i.e., the 2 boys), what you don't consider your business (her stupid flirtation with band members at the age of 37 -- um, grow up! 'Cause they ain't flattered, they're laughing). And tell her in no uncertain terms that you will discuss the In-Bounds topics with her civilly, but you absolutely refuse to engage the Out-of-Bounds topics, Full Stop.
Of course, you're going to have to be prepared to walk that walk. But if you don't you'll lose your sanity. Just look at me -- I'm writing this from inside a padded room....
