To me, the subtext of that conversation was Lu and the others saying, "I can't believe you are essentially quitting the show mid-season." It seems pretty clear to me that the conflict between Tins and Scott was over her being on the show. And if he wasn't going to commit, then she wasn't going to leave the show. But given all of the abuse she has taken from Dorinda this season, it sounds to me like she flew out to Chicago to say, "if you commit, I will leave the show immediately and move to Chicago." Basically, IMO, Dorinda's behavior gave Tinsley the impetus to get the hell out of dodge, and I don't think that she was there before.
I give Tinsley for leaving basically on her own terms. Usually these housewives are hanging on for dear life, whether it is because they need the money or because they become addicted to the limelight. And unlike, say, Lisa Vanderpump and/or Denise, Tinsley didn't just "stop filming," she just jumped and therefore got to dictate the way her leaving is being portrayed. Dorinda can claim that Tins is "stupid," but the fact is that she found a way to have far more control over the situation than Dorinda will ever.