My gut is telling me to maintain the moral high ground, say nothing, move on from my WW (just waiting for the separation papers to be finailized) and let her web of lies unravel all on its own. That will be the greatest revenge as I won't have to do anything.
IMHO You say this but it just looks like a PU$$Y way out of avoiding the problem and helping out another person who is also betrayed.
In the future, don't be upset if somebody doesn't lend you a helping hand when they know of something harmful that could happen to you. You wouldn't want them to compromise their moral high ground.