Eh, still doesn’t change that she's the third party/side hoe. If her family has enough clout to investigate an upload of a candid photo, sis has enough resources to get a background check on her hubby, once his other affair came to light.
Besides, once the truth came out, she had the choice of breaking up with him. She didn't. Love isn't a defense for cheating, and will never be.
So for all its worth, I think laser-guided karma might strike her. The guy moreso, since he's the worst of the two.