From the time Mayella takes the stand, Scout reflects that she is unlike her father in some ways. While Bob Ewell is filthy, Mayella seems to try to keep herself clean. Scout associates this with the red geraniums she tries to grow to bring a bit of beauty into her life.

When Mayella, who is not a child but a young woman, begins crying on the stand, Scout and Jem don't know what to make of it. After all, their father is always kind and respectful, and they have always seen people react to him positively based on this reputation. Scout wonders if Mayella has "good sense," and Jem wonders if she's just trying to get the judge to feel sorry for her.

Scout also notices that Mayella acts especially nervous on the stand, first twisting a handkerchief into a "sweaty rope" and then trying to get her story straight:

Mayella was silent. She seemed to be trying to get something clear to herself.

Although Scout notes that it causes Atticus physical pain to bring the truth of Mayella's situation to the knowledge of the court, Mayella nonetheless lashes out at him one final time before refusing to say another word. It is at this point that Scout realizes how "poor and ignorant" Mayella really is. Her situation is so dire that even the judge fails to chastise her the way he should.

In short, Scout and Jem have never encountered a woman like Mayella, and they have a difficult time processing both her tragic situation and her erratic personality on the stand.

The children are both initially dubious about Mayella Ewell’s character and her testimony. The fact that she is evidently more accustomed to bathing than her father makes something of a good impression on Scout, but neither Scout nor Jem knows what to make of her outburst of tears. Jem observes that she has “just enough sense to get the judge sorry for her.”

When Mayella reacts with indignation to Atticus’s courteous words, however, Scout feels sorry for her too. She feels rather more pity, in fact, than Judge Taylor does. She wonders what Mayella’s life is like, and quickly discovers that it is very hard. Scout’s pity is awakened by the combination of Mayella’s evident ignorance and hostility, and the revelations about the abuse she is forced to endure at home.

Mayella cuts a pathetic figure in the witness box. She is continually tearful, angry, and suspicious that she is being mocked and talked down to. Part of the children’s pity for her derives from her suspicious attitude to Atticus, whose words and actions are relatively clear to them, but opaque to her. Although Mayella is nineteen, her lack of education and her evident fear of the proceedings make her seem much younger than this to Scout and Jem, who understands what is going on much more clearly than Mayella does.

In chapter 18, Mayella Ewell takes the witness stand, where she proceeds to lie about being assaulted and raped by Tom Robinson. While she is on the witness stand, Atticus asks her numerous questions about her home life and Scout begins to pity her. Scout discovers that Mayella has no friends, rarely leaves her home, lives with an abusive father, and is forced to raise her siblings. Scout exercises perspective by standing in Mayella's shoes during her testimony and has sympathy for her. As Atticus continues his cross-examination, Mayella begins to contradict her testimony and it becomes evident that she is lying. Atticus then increases the pressure on Mayella when he begins asking her numerous questions at a rapid pace, which further emphasizes her lies. After Atticus's cross-examination, Scout mentions that she feels numb and looks over at Jem and Dill, who are both yawning. Apparently, Jem and Dill did not find Mayella's testimony riveting and Jem proceeds to explain the finer points of the trial to Dill during the brief recess.

Scout pitied Mayella.  She found Mayella to be ignorant, and she knew that she was poor.  In fact, everyone in the Ewell family was poor.  Scout seemed to be the most moved out of the three children by Mayella's story.  Dill and Jem yawned when Mayella finished testifying.  They did not react otherwise.  

When Atticus began questioning Mayella, he treated her with politeness.  He addressed her as he would any lady.  Scout observed that Mayella may have never been treated in such a respectful way before.  Mayella was offended by the polite words Atticus used.  She thought he was making a mockery of her.  Scout knew her father well.  She knew that he treated everyone with respect.  Mayella was no different.  As she listened and watched, Scout "wondered if anybody had ever called her 'ma'am,' or 'Miss Mayella' in her life; probably not, as she took offense to routine courtesy" (To Kill a Mockingbird, Chapter 18).  When Mayella was finished speaking, Scout "discovered that [she] had been sitting on the edge of the long bench."