Mayella Vilot Ewell is the secondary antagonist of To Kill a Mockingbird. She is the eldest daughter to Bob Ewell, the antagonist of the novel. She's the reason as to why Tom Robinson is taken to court, and was indirectly responsible for Atticus Finch's involvement with her case.
Mayella was a 19-and-a-half year old woman who was forced to take care of her other siblings, because of her father's alcohol addiction. Throughout her life, she was shown no love by any of her siblings nor her distant father. Her relationship with her father was most likely even worse because it's heavily implied that Ewell raped her, and that she's most likely the mother of all of her siblings. When Tom told his version of events that happened on that November day, Tom states that when Mayella forcibly kissed him, she said that it was all right because no other man kissed her before, and that the things that her father did to her didn't count. Her need for love was so great, that she went against the town's civil code, and she seduced Tom Robinson while she was alone with him in her house. Ewell discovers what his daughter was doing with Tom, and threatened to kill her. In response, Tom runs away out of fear. In his rage, Ewell severely beats Mayella, and he leaves the right side of her face bruised. Later on, Ewell charges Tom with beating his daughter, and then violating her. This incident sets up the plot up ahead.
When Atticus asked Mayella to come to the stand, she appeared to be nervous. When Atticus was casually speaking politely to her, Mayella jumps at him and accuses him of taking advantage of her. After telling her side of the story as to what happened on that night on November 21, she accuses all the white gentlemen of being cowards if they don't find Tom guilty. After Mayella had seduced Tom that November day, she was trying to hide her guilt by destroying Tom. With Tom out of the way, she could cast aside her guilt.
Atticus later asked Bob Ewell to come to the stand and write his name on an envelope. Bob does so, and when he does write his name, he wrote his name using his left hand. Tom couldn't use his left arm because of a cotton gin incident, so with Bob writing his name with his left hand, it gives the jury members the proof that they needed to who really beat Mayella. However, despite Atticus' deductions, Tom is found guilty anyway because an all white jury wouldn't find him innocent. He's sentenced to death.
Mayella is last seen aiding her family at chunking rocks at Helen, the wife of the late Tom Robinson. After Ewell's death, whatever happens to her and Ewell's other children is not brought up.