|G=Grandmother, PS=Pitty Sing, B=Bailey, M=Misfit|
One last comment: This is totally not a definitive plot diagram of the story--I'm even sure there are much better ones out there--but if you are reading to write, like me, this is a really great exercise. It makes you define the essence of the story. To me, the essence of this story is about the Grandmother's inability to recognize evil, whether in herself or others. That's why I identified the crisis point (the highest point in the diagram) as when the Grandmother mistakes the Misfit for one of her own children--this ultimate blindness results in her death.
Whether this is the "right" or "wrong" idea, I leave up to you. But I can promise that using these diagrams will help you figure out your own conclusion, and at the very least, you'll discover how tight (or loose) the plot is in your favorite stories.