When Mayella Ewell begins to testify and Judge Taylor simply asks her to tell the jury what happened, she bursts into tears. When Judge Taylor asks her why she is crying, she claims to be afraid of Atticus and says, "Don’t want him doin‘ me like he done Papa, tryin’ to make him out lefthanded...” She is referring to Atticus's strenuous cross-examination of her father, Bob Ewell, and Atticus's forcing Mr. Ewell to admit that he is ambidextrous and could have hit Mayella with his left hand.
Mayella may be afraid of Atticus, but she may also be crying to get the judge and jury to feel sorry for her. Jem says of Mayella, "She’s got enough sense to get the judge sorry for her." In other words, crying may be a tactic she uses in court to get pity. Perhaps she also feels sorry for the perjured testimony she is about to give, in which she is going to lie and help convince the jury that the innocent Tom Robinson is guilty. Mayella truly cares for Tom, and perhaps she has enough decency to feel sorry for lying, even if she knows that fear of her father and of what the white community would say about her cause her to lie.