Describe Mrs.Walker. What are her two mains sins? What do you think happened to her when she disappeared? Did she deserve that fate? Symbolically, what do you make of the heart and liver that were left behind?
Mrs Walker is described as being just as miserly as Tom, and spends most of her time attempting to cheat and deceive him. She has no obvious job, nor does she appear to have any hobbies, interests, pastimes or friends. This casts her as a somewhat one-dimensional personification of greed, although that may simply be a choice to suit the author's purpose.
Classifying sins is a fairly subjective task, but if we were to go by the famous "seven deadly sins", then her two greatest sins are greed and wrath. While we could easily make a case for her exhibiting lust and envy as well, greed is what inspires her to try to make a deal with Scratch on her own, and it is her wrath (uncontrolled anger) that gets her killed; she doesn't control her temper well enough to realize that picking a physical fight with the embodiment of evil is probably a bad idea.
The question of whether Mrs. Walker deserved this fate is uncertain. Does anyone deserved be killed by the Devil, and have their heart and liver tied up in an apron? It might be better to ask if her fate is surprising, considering the way she lived her life.
Symbolically, the heart and liver have many and mixed meanings, and the exact one intended here is not explicitly stated, if in fact there was any intended meaning as opposed to Irving just attempting to shock his audience. The heart symbolizes emotion, the life force, and love, while the symbolism of the liver is somewhat more obscure, but is often tied to similar qualities, and its functional role in the body is purification. We might interpret that Scratch left these items behind either because they were offensive to him, being associated with love and purity.