So far I have geraniums, a knife for her dad who died, a picture of tom robinson and a nickel for the kids she cares about. I need something to represent the trial in which she wrongly accusses Tom Robinson but, i'm not sure what could represent the trial.
Mayella may have kept a magazine with images of how she would like to be, or maybe a scrapbook of some type, with pictures of gardens, neat houses and all the things that she did not have a chance to enjoy.
Outside of the excellent ideas you have already, and the suggestions made by post #2, I would suggest a gavel, a piece of a rag (symbolizing her cleaning), and lipstick (symbolizing her femininity and desire to be wanted). You may even consider creating a fictional diary of Mayella's to include.
You have some excellent choices so far. The dried geraniums are a must, although I don't really think I'd add the photo of Tom, since she most likely would like to forget about the mistake she made with him. You might add pictures of Mayella's mother and brothers and sisters, and perhaps a newspaper story about the trial, Tom's death, or her own father's obituary.