In Harper Lee's To Kill a Mockingbird, Aunt Alexandra is very representative of the Old South. In fact, we can even consider her to have been a Southern belle in her youth, a young, unmarried woman representative of Southern upper-class society, and she still displays her Southern belle characteristics. Therefore, she fits in with Maycomb society as one of its leaders.
We know Aunt Alexandra embodies a Southern belle because she is descended from Simon Finch, founder of Finch's Landing, who died wealthy. In fact, Aunt Alexandra still lives at Finch's Landing, a farm upon which stands a very large house built by Simon Finch, described as having six bedrooms. In Chapter 13, we also learn that she "owned a bright green Buick and a black chauffeur," another sign that she was and still embodies a very wealthy Southern belle.
As a Southern belle, she has very strict notions about how the Finch children should behave. Aunt Alexandra is constantly ridiculing Scout for her boyish behavior and attire and, in Chapter 13, comes to live with the Finches to give Scout "some feminine influence" since, soon, Scout will be old enough to "become interested in clothes and boys—." In addition, she feels that children of "gentle breeding," like the Finch children, should take pride in their family heritage and always behave like ladies and gentleman.
Once she settles into Maycomb, Aunt Alexandra, having been a Southern Belle, presumes a feminine leadership role. Aunt Alexandra exhibits her leadership role by leading a Missionary Society and becoming Secretary of the Maycomb Amanuensis Club.
Aunt Alexandra, as Scout notes, fits perfectly into Maycomb society. Maycomb is generally a conservative community which holds rigid notions about the way people ought to behave, laying down divisions between people of different social class, race, and gender. Alexandra is the same. Her prim and proper notions about how ladies ought to behave makes for much comedy between her and the rebellious, overall-wearing, tomboyish Scout. She is also disapproving of Scout's mixing with people of lower class and with blacks. Good breeding is a matter of the utmost importance to Alexandra and she always strives to instil a sense of family pride in Scout and Jem, although she isn't particularly successful.