With all due respect to the poster and to the one person answering so far, I don't see how anything in Mayella's testimony proves that she's lying. What we have when we read the trial scene in To Kill a Mockingbird is a set of conflicting first-hand accounts. The fact that Tom Robinson's account contradicts Mayella's does not prove the she is lying and he is not. The novel sets us up to side with Tom Robinson; the Ewells have consistently been presented to us in the narrative as despicable humans and the Robinsons as upstanding citizens.
My point is not that the two of you are wrong! Not at all! I simply wish to point out a very clear bias in the narrative that we, as readers, can resist. There's a very similar bias in the discussion of birds, for example; "you can shoot all the blue jays you want," we're famously told, "but remember it's a sin to kill a mockingbird." In reality (ask a real bird expert!), mockingbirds can be extremely aggressive and territorial just as blue jays have their own important ecological niche. Reading as a "resistant reader" is a good way for us to move past the same, standard interpretations of a literary work.
To me, Mayella may or may not be lying, but she's certainly very much aware that she's in a sticky situation and asks repeatedly for clarifications to Atticus' answers. (I've always wondered, for that matter, about her comments about her father and Atticus' follow-up questions. Does he avoid bringing up questions about incest or domestic abuse because he finds them untasteful, or does he simply not see that as a possibility?)
First of all, we can assume that Tom is telling the truth: Mayella invited him inside her house, he climbed up on a chair, she hugged him and kissed him, and he tried to pull away. When he finally did, he got out of there as fast as he could. Many of Mayella's statements contradicted Tom's testimony, and even some of Mayella's testimony did not mesh with her father's. Examples:
- Mayella claims Tom came up behind her and grabbed her neck. It was actually Mayella who grabbed him.
- Mayella claims Tom cussed at her and "hit me agin an' agin."
- She testified that he "chunked me on the floor an' choked me'n took advantage of me."
- Mayella swears that her father has "never touched a hair o'my head in my life."
- She later retracts her statement that Tom had beaten her, then changed her mind, and then said that "I just don't remember."