Aunt Alexandra's presence in the Finch home is to demonstrate a contrast in something. What is it?To Kill a Mockingbird by Harper Lee
Attitudes within a family can differ. On the one hand, Aunt Alexandra acts as a foil to Atticus as she represents the stereotypical upper class white woman of the South in the 1930s. She is a member of one of the more prestigious churches of the town, her family has a prestigious ancestry of which she is very proud, she has been refined in all the social graces, and she possesses the typical attitude about race and class for her social status.
When she arrives at the Finch home, she exerts efforts to counteract her brother's liberal influence. She does not allow Calpurnia to bake he tea cakes for her Sunday Missionary meetings with the other ladies of the community, and she forces Scout/Jean Louise to wear a dress. When she learns that Calpurnia has taken the children to the black church, she is appalled. And, she discusses various matters with her brother, urging him to "let this cup pass" regarding his defending of Tom Robinson. In addition, she scolds Atticus about allowing the children to be so free.
On the other hand, Alexandra does demonstrate kinship with Atticus. In private she disapproves of the hypocrisy of the women in her missionary circle. A loving sister, she is also kind like her brother and becomes incensed at the cruelty of the jury. She, too, has a sense of fairness that is obviously intrinsic to the Finches.
Aunt Alexandra views herself somewhat as a savior to the Finch family name. As an extreme heretic, her supercilious views constantly refer to how she values the background of the Finch family and lives to preserve that name.
Defending an African-American is of the unspeakable to Aunt Alexandra, as the Finches were once a slaveholding family. Atticus becomes an iconoclast in that he refuses to uphold slaveholding traditions that were honored in his past. He is revolutionizing both the Finch household as well as the society of Maycomb by refusing to accept the racial injustices that are accepted as a daily occurence in Maycomb.
Aunt Alexandra is aware of Atticus's opposing views yet imposes dresses on Scout and attempts to make her a 'lady' and firmly disagrees with the children's love for Calpurnia. Aunt Alexandra is constantly concerned with her social status and can think of nothing more, at some times it appears, especially when it comes to associating themselves with anything or anyone that seems in the slightest bit inferior to her and her family. For example, she prohibits the children from seeing the Cunninghams and associating themselves with African-Americans in general because they are 'trash'. She states that they are not their 'kind'. However, as the novel progresses, Aunt Alexandra appears to be bound by her title and label as a respectable lady who will not associate herself with 'trash' while she secretly wishes to speak out and defy the hypocrisy which is occuring within her missionary society group.
However, it may be that she uses this excuse simply to watch over the family. Though it is not shown daily, Aunt Alexandra greatly cares for Atticus which is shown in the way she consults Miss Maudie about what actions she should take in order to relieve Atticus's pain about the loss of the trial. After Bob Ewell's foolish action of outrage, she also grows worried about the welfare of Scout and Jem and doubts their safety in the streets of Maycomb with the mercurial Bob Ewell.