Alexandra may be Atticus's sister, but she does not share his vision of social or racial equality. She considers African Americans as second-class citizens, and she certainly doesn't believe that they are privy to all discussions in the home, even if Atticus does consider Calpurnia a "faithful member of this family." Alexandra is upset with Atticus for commenting that newspaper editor B. B. Underwood
"... despises Negroes, won't have one near him"
in front of Calpurnia. Alexandra believes that Calpurnia will soon spread the word among her black friends--"You know how they talk among themselves"--and this is information that Alexandra believes is unfit for Negroes to know, even though Atticus assures her that
"I'm sure Cal knows it. Everybody in Maycomb knows it." (Chapter 16)
Alexandra claims that such talk "encourages them," and that allowing black people to be accessible to this information-- public knowledge--will assure that
"Everything that happens in this town's out to the Quarters before sundown." (Chapter 16)