Mayella Ewell is definitely a young woman deserving of some pity in To Kill a Mockingbird. She is stuck with an evil drunkard of a father who beats her and possibly even takes advantage of her sexually. With her mother dead, she is forced to raise the remainder of the Ewell clan herself. She has no friends, no money and no prospects for the future. She asks Tom to come to her house out of loneliness, and she later tells him that she has never been kissed, so "she might as well kiss a nigger."
Of course, Mayella is still guilty of framing Tom for her supposed rape. No doubt it was her father who did the beating after catching her with Tom, but she still bears the responsibility for going along with the story that her father has concocted. Her fear of her father left her with little choice.