I agree with mildas above that there seems to be a lot of information missing in Mary's history with her relationship with Leonard and maybe even some misinformation regarding what her sister thought she knew of her. According to Peggy, Mary was independent- -a feminist even--working hard to raise a chid on her own. So what would possibly cause her to be attracted to someone like Leonard in the first place???
I am embarrassed to admit that I struggle to feel compassion toward Mary, in spite of the fact that she is an emotionally abused woman. She lived a different life before Leonard. She cared for and loved Jeremy. She and her sister created a safe, nurturing environment together. So what switch was flipped that caused her to choose someone so extremely opposite from her and abandon everything about herself? And I absolutely do not understand (or even like) anyone who chooses a church or vengeful God who directs you to kick your own child out of his home because he is gay. The God I know and understand would never ask a parent to turn his back on his child. So I probably wouldn't have told Mary to leave her husband. I most likely would have asked her what in the hell she was doing marrying him in the first place. So I'm asking myself, "wow is it possible to not really like someone who is herself abused?" (And believe me, I'm feeling a bit guilty for writing off Mary's suffering under Leonard because of what she allowed it to do to Jeremy.)
In my opinion, Mary testified because "I don't want to go to jail, Leonard" not because she loved her son and wished she had done things differently with regard to Jeremy. Her testimony evoked no strong feelings of love for her child or pain that he had been living on the streets or regret that because of her lack of action as his mother he was now on trial for murder. In the big picture, the actual murderer was a better witness than Jeremy's own mother!