I'm missing something. This ONLY is an issue in YOUR family because YOUR wife decided to have an affair with this woman's husband. Correct?
If she tries to push this off on you, I suggest you push it right back. In fact, I'd suggest you then play OFFENSE, and get upset with HER for being dragged into these people's lives, and into court!
"Never rescue an infidel from the consequences of their infidelity."
