Mary Winkler was convicted of Voluntary Man Slaughter which means that the jury believed that the crime was committed in an irrational state of mind. I think I would have made the same judgment. Of course, I didn't hear all the testimony, but I think that the prosecution's arguments for premeditated murder were weak. Any prosecution is going to parade a bunch of people with glowing stories of the minister whom they didn't know as well as his wife. Anyone who is married or in any other close relationship knows that your partner knows aspects of you that no one else ever sees. This is one of the things that makes marriages and other close relationships special. Sometimes that exclusive knowledge is about unpleasant things that nobody else should know.
This is the Matthew Winkler that Mary knew, the secret "bad" Matthew, the one who demeaned her emotionally and sexually. Of course, she's not going to go around telling people that their minister is a pornography-driven pervert. She was the good Christian wife who never complained openly about her marriage and who would never speak about her sex life.
As a Tennessean I think it's safe for me to say that I know how these jurors reacted to this situation. We all have a kind of common cultural knowledge of how things are, so predicting their way of thinking isn't too hard. That the jury only took 8 hours to deliberate is good evidence that they were in pretty close agreement from the beginning of the deliberation. Overall, the whole case and trial moved quickly, and quick justice is good justice.