What details are revealed about Mayella Ewell during the trial?

Before Tom Robinson's trial at the courthouse, not much was known of the Ewells, and even less of Mayella. The only specific mention of knowledge of Mayella before the trial was the description of the beautiful geraniums she cared for in their ramshackle front yard. During her testimony, Atticus first asked questions to paint a picture to the jury of the Ewells' home life. From that, we learned that Mayella was 19 years old, the oldest of eight children. Their mother passed away when she was young, leaving Mayella to become her siblings' surrogate mother and (possibly) her father's surrogate wife. She only received two or three years of schooling, as her father decided that, with the two of them being literate, there was no need for the rest of the children to go to school. Even though the family received welfare checks from the county, there wasn't enough money to feed the whole family, especially after Mr. Ewell spent the money on alcohol. The children had to rummage through the garbage heap for food. We learn that Mayella doesn't have any friends, and Atticus suspects that Mr. Ewell abuses and possibly molests her, despite her assertion that “My paw’s never touched a hair o’my head in my life".

During the various testimonies, it became clear that there were discrepancies between the Ewells’ story and the apparent truth. Atticus got Bob to admit that, despite her being allegedly beaten and raped, no one thought to get Mayella a doctor. This was suspicious, because it meant there was no medical documentation of her original injuries. Mayella left holes in her testimony. At first she claimed the encounter in question was the first time Tom was in her yard, but then admits she “might” have invited him before, but couldn’t remember. Her memory was also unclear regarding whether or not she specifically recalled Tom hitting her in the face. She had no answer to why none of the other children were witness to the event. When Tom testified, he revealed that Mayella had hired him for “odd jobs” many times, that she had sent the other children out for ice cream, and that she had tried to seduce him against his will, only to be discovered by Bob, causing Tom to run away. The most damning discrepancy was that Bob was proven to be left handed, and that Tom Robinson’s left arm was lame. Scout observed: 

His left arm was fully twelve inches shorter than his right, and hung dead at his side. It ended in a small shriveled hand, and from as far away as the balcony I could see that it was no use to him.

This evidence made it almost impossible for Tom to have been responsible for Mayella’s injuries.