Scout asks Aunt Alexandra if she's come for a visit, and aunty says that she and Atticus have decided that it's best if she stays with them for a while, as Scout needs some "feminine influence" (13.10).
Scout does not agree with this, but keeps quiet about it.
In fact, Scout has trouble making any kind of conversation with her aunt.
That evening Atticus comes home and confirms Aunt Alexandra's reason for her coming to stay, though Scout thinks it's mostly her aunt's doing, part of her long campaign to do "What Is Best For The Family" (13.22).
Aunt Alexandra is popular in Maycomb and takes a leading role in the feminine social circles, even though she makes obvious her belief that Finches are superior to everyone else (even though, as Jem says, most people in town are related to the Finches anyhow).
Aunt Alexandra is a firm believer in Streaks—each family has one (a Drinking Streak, a Gambling Streak, etc.), though Scout doesn't really understand her aunt's obsession with heredity.
It makes a kind of sense. The town is far enough away from the river that forms the area's main transportation route means that hardly anyone ever moves to Maycomb or away from it. Families have known each other for generations, establishing the reputation for having "streaks."
Scout mostly ignores her aunt, unless she gets called in to make an appearance at a luncheon or tea.
Alexandra also attempts to instill family pride, by, for example, showing them a book their cousin Joshua wrote.
Unfortunately, the kids already know his story from Atticus: he went crazy at college and tried to assassinate the president of the school.
After this Aunt Alexandra sends Atticus to talk to the kids about being proud of their superior heritage, but he just scares them because he doesn't usually talk to them in that way.
Scout ends up crying on his lap, and Atticus tells them both to forget it.