If we interpret Mary Dempster along Jungian archetypes, we see her in various roles and see her as a dynamic character who changes as much as Dunny does in the novel since she is arguably, one of the active agents for change in Dunny's life. Firstly, she is the mother figure, brining forth a weakened child into the world. She then becomes a type of a saviour figure, not only because of her appearance to Dunny as he crawls through the mud in WWI, but also because she gave of herself unselfishly to the drifter in the gravepit. After this incident she is not crazy, but distracted. She becomes the jungian outcast in the novel since the small town mentality cannot accept why she would ever prostate herself to a drifter. Mary becomes other things through the novel. This is just a start. The point is that Mary Dempster cannot be dealt with so tritely. She fills a complicated function in the novel so we should have many opinions about her.
well in the book the town people refer to her as "simple"
however this was before the gravel pit inncident.