You seem to be trivializing a few things involved with Kittie...
I understand that on this forum,this wil be un-popular. I was going to bow out before speaking what seems to be obvious truth. I am must say it is disappointing to see such un-balanced opinions be given to her. But if we put aside our dislikes and baises we will see Kitties story for what it is. After I came to the conclusion that Kittie did ask for this type of discussion, I will interject here. Couple points in the story that were missed:
A.) Her Mom does not "shun" her D'fd sister, why? Obviously that suggests some nuances to this and probably Kittie has some issues she is not telling us. From her Moms POV, Kittie is ruining her life, maybe she has supported her mistakes in the past and she is at wits end? Maybe she is not the terrible Person after all.
B.) She did not say she made a mistake, but had an affair, which is different than simply just succumbing to "manly sin". This is knowing you are doing wrong, potentially playing a part in messing up the pysche of another human being, causing strain in the marriage of another etc..etc.. Sorry, even apart from Christianity, this is bad, abhorrent behavior. She knew she was doing wrong, and she simply could not help it. This is a destructive personality trait that needs to be corrected. The pattern will repeat. I must say I am disappointed by the lack of thought that has gone into the "way to go Kittie" help you are giving her. You are living with some guy you love now, not married to him I gather..... Sorry to sound so conservative here, but we now how this story ends. She will be 35 before she figures this out. That is sad.
As someone newly married, I am thinking about Kitties story, and thinking how I would feel if My mate cheated on me, or if I cheated on her. You can't do stuff like that. You got to clean that mentality up.
C.) Not shunning D-fd family is not a rare as you think, I can think of others in my own congregation. Maybe having your "JW world" be guided largely by the internet has skewed the Reality? The persons demeanor toward "mistakes" go along way.
Sorry to add the more proper view here, but it has to be said.