In To Kill a Mockingbird by Harper Lee there is no actual rape of Mayella Ewell, of course. The charge of rape is issued against one of the novel's mockingbirds [who must sing another's song], Tom Robinson, who simply tries to offer some assistance to Mayella.
In passages, however, there are a few allusions to Tom's case and the charges. For instance, Atticus is heard on the phone remarking on the hysteria of the town as the charges have gone from more innocuous ones to rape, and in Chapter 14, Scout asks Atticus what rape is, for she has overheard people in a crowd as they shop:
'They c'n go loose and rape up the countryside for all of 'em who run this county care,' was one obscure observation we met head on from a skinny gentleman when he passed us.
The description of Mayella's so-called assault comes from Sheriff Heck Tate as he testifies in Tom Robinson's case. He describes the bruises on Mayella's face and arms as well as the marks on her neck. These marks, of course, have been made by her own father, who became apoplectic when Mayella kissed Tom.
We do not actually "see" Mayella getting raped (or whatever it is that truly happened to her) in the book. Instead, we are only told what has happened via testimony in court. The courtroom scenes that include testimony about what might have happened to Mayella start in Chapter 17.
In Chapter 17 and in the next two chapters after that, we hear various people's testimony as to what happened. By the end of the testimony it seems pretty clear that Mayella's dad is the one who beat her and that Tom Robinson did not rape her.