[Atticus probes her about this, and Mayella almost said that her father….abused her when he drunk, but stops herself just in time and says nothing]

We also learn that she was very lonely, as she had no friends(she didn’t even understand the word when Atticus asked her).

[evidence about Bob Ewell being left-handed shows, because someone left-handed hit Mayella, that he was obviously the one that inflicted the injuries on the right side of her body]

Ninjas=Full of phail 😛

but anywho, Mayella’s testimony revealed that she was lying. It also indicates that she was possibly abused by her father. It also shows how lonely she is, and how she tries to better herself(symbolized by the flowers)

Thats only a bit.

Find the rest out on wikipedia like the rest of us.