Later in the book, Atticus says he has “pity in my heart” for Mayella. Why?

Mayella is a victim. Atticus knows this. He knows she is abused by her father physically, emotionally and sexually. If you read between the lines it is evident that the children running around the Ewell land belong to Mayella and her father. I know, yuck. Atticus knows Mayella is controlled by her father and leads a most pathetic existence.

At the same time, Atticus says that his pity "does not extend so far as to her putting a man's life at stake, which she has done in an effort to get rid of her own guilt." I say that Atticus has pity for Mayella, but also does not pity Mayella for what she's done to Tom Robinson. Atticus pities Mayella because of her trauma. She is being abused by her father and she can't do anything about. Mayella is a victim of verbal, mental, and (yes) sexual abuse. You can even see this verbal and mental abuse even in the courtroom when Atticus asks Mayella if she loves her dad: "' Do you love your father, Miss Mayella?' was his next. 'Love him, whatcha mean?' (this is important because it shows that Mayella doesn't know the true meaning of love; just keep that in mind) 'i mean is he good to you?' 'He does tollable, 'cept when-' 'Except when?' Mayella looked at her father, who was sitting with his chair tipped against the railing. He sat up straight and waited for her to answer... 'Except when nothin',' said Mayella...Mr. Ewell leaned back again." Mayella's dad is pretty much controlling her, and she can't even say what's true or not. Even if she said the truth, the consequences she would face would be (potentially) deadly. If you think about it, Tom Robinson is one of the mockingbirds of the story, and Mayella blindly shoots him with her dad having been the one who pulled the trigger.