Atticus' sister, Alexandra, comes to Maycomb in order to take care of Jem and Scout during the Tom Robinson trial, but it appears that she plans to stay much longer than that. Atticus had not told the children about her arrival, so it was a surprise to them. Alexandra explained that
"We decided that it would be best for you to have some feminine influence."
Scout knew that "There was a story behind all this," and she waited to hear Atticus' explanation. His answer was not much clearer, for Scout was left "not understanding a word he said."
Atticus had apparently gotten tired of his sister's nagging about how unladylike Scout had become, and he finally gave in to her request to "stay for a while." Since Alexandra did not get along with her husband, Jimmy, it could be that she was also lonely in her isolated Finch's Landing home and yearned for the social life that Maycomb offered.