What is the essence of Mayella's testimony in To Kill a Mockingbird?

Mayella claimed during her questioning by Mr. Gilmer that
she had asked Tom Robinson to come "bust up" a chifforobe for her for which she had
offered him a nickel.  Her fictional testimony at this point gets a little fuzzy: She
ran into the house to get him the nickel, she said, and he ran up behind her and had her
around the neck and was hitting her.  She fought "tooth and nail," but she claimed to
have fainted at some point and was sure she was assaulted during her time unconscious,
because, in her words, "he done what he was after."  During Atticus's cross examination,
it becomes known that Mayella is basically illiterate, doesn't know exactly how long her
mother has been dead, doesn't attend school or have friends, and despite her efforts at
evading the question, she more or less acknowledges that her father hits her when he's
been drinking.