Aunt Alexandra makes it a point to fit into Maycomb's social life. When she moves in with Atticus and the children, she tries to get them to acknowledge their family history, particularly with respect to their social position.
Aunt Alexandra fitted into the world of Maycomb like a hand into a glove, but never into the world of Jem and me. I so often wondered how she could be Atticus’s and Uncle Jack’s sister that I revived half-remembered tales of changelings and mandrake roots that Jem had spun long ago. (Chapter 13)
Atticus is very liberal and honest with Jem and Scout. Atticus informs them of the social structures of Maycomb but he certainly does not endorse the ways people use those structures to keep certain groups (namely, African-Americans and the poor) in socially and economically disadvantaged positions.
Alexandra, on the other hand, wants to uphold these social structures and the class positions that they form. There are moments in the novel when she shows a more open-minded perspective on things (her reaction to the news of Tom's death) but she is willing to put that perspective aside when it comes to upholding social traditions. For example, she recognizes the hypocrisy of her missionary circle but it is a tradition of Maycomb's "ladies" so she continues to participate in it.
Alexandra overtly reveals her loyalty to these traditions when she calls Walter Cunningham Jr. "trash" and forbids Scout to associate with him.
"The thing is, you can scrub Walter Cunningham till he shines, you can put him in shoes and a new suit, but he’ll never be like Jem. Besides, there’s a drinking streak in that family a mile wide. Finch women aren’t interested in that sort of people.”