How does Mayella incriminate her father on the witness stand in To Kill a Mockingbird?

As Chapter 18 of Harper Lee's novel To Kill a Mockingbird begins, Mayella Ewell, the grown daughter of the town's most virulently racist and repugnant individual, is called to the witness stand in the trial of Tom Robinson, the African American accused of raping Mayella. In the previous chapter, Bob Ewell, Mayella's father, testified that he heard his daughter screaming and saw Tom run away. From the opening chapters of To Kill a Mockingbird, Lee's young narrator, Scout, has noted that the Ewell family is distinguished by their abysmal hygiene and disdain for education. Bob, the father, is a drunk and a racist, and he is known for the manner in which he raises his children, with Mayella, the oldest, forced to bear the burden of providing what domestic stability exists while her father drinks away what little money they have. When, in Chapter 17, Bob Ewell testifies in the rape trial, he is disrespectful towards the court and, it is assumed and later validated, lying despite being under oath.

When Tom Robinson's defense attorney, Atticus Finch, is presented with the opportunity to cross-examine Mayella, he is able to draw out of the uneducated, ignorant young woman the fact of her father's abusive nature--key to undermining her claim to have been raped by Tom. Atticus knows that it was physically improbable if not impossible for his client to have  raped the full-grown and physically formidable Mayella, as Tom, it will be revealed, has a crippled arm. Atticus also strongly suspects that it was Bob Ewell himself who beat and possibly raped his daughter. His task, then, is to draw out of Mayella the truth about her father, despite the fear she holds of Bob's retribution should she fail to stick to her highly improbable story. The first instance of this occurs with the following exchange:

In "To Kill a Mockingbird", where does Mayella admit her father's abuse?

When she's put on the witness stand in Chapter 18 of To Kill a Mockingbird, Mayella doesn't explicitly says that her old man's abused her. Apart from anything else, she's too scared to reveal the truth in open court; she knows what Bob will do to her if she opens her mouth. But then Mayella doesn't really need to say anything; everyone in town knows what her father's like. They know just what a vile excuse for a human being he really is and how badly he treats his own daughter.

Even so, the jury are still prepared to believe that it was Tom Robinson, and not Bob Ewell, who attacked Mayella. That's because they are mired deep in racial prejudice. Even though there's no evidence against Tom; even though he was physically incapable of committing the crimes for which he's been accused, he's still convicted. The Ewells may be the most despised family in town, widely looked down on as "white trash," but they still have one advantage over Tom Robinson: the color of their skin.