Only at one point do we see Calpurnia as a "stereotypical" black woman in this novel. That is when she takes the children to her church, First Purchase. Lula confronts her about bringing "white chillin" to her "black church," and Cal replies with a different dialect and voice than what the children are used to. In order to live in both worlds, Cal must behave in certain ways in front of both sets of people.
Harper Lee definitely calls into question these stereotypesby using Cal as one of the strong female influences in the children's lives. She is well-educated, and more importantly, she serves as a "mother" figure to a white family. Most black women would never have the opportunity to work in a house and fit in as well as Cal does with the Finches. Lee keeps Cal as a minor character, but she plays a very important role, which helps to dispel the prejudice found everywhere else in the novel.