Atticus's sister Alexandra arrives in Maycomb with her suitcases in Chapter 13 of To Kill a Mockingbird.
When Scout inquires of her aunt if she has come "for a visit," Aunt Alexandra seems surprised. "Didn't your father tell you?" She then informs the children that she and Atticus have decided that it is appropriate for her "to stay for a while" because Jem and Scout are "growing up," and it would also be good for the children to have "some feminine influence." Alexandra's phrases imply that Scout should not be punching boys in the mouth as she did Francis at Christmas, and she should be wearing dresses and learn the social graces.
Aunt Alexandra also is concerned that during the summer the children are alone with only Calpurnia to care for them. Atticus himself is anxious about this coming summer because, as he tells Scout, "I can't stay here all day with you, and the summer's going to be a hot one." So, Aunt Alexandra will be at home for Jem and Scout.