Why is Aunt Alexandra angry in To Kill a Mockingbird?

In To Kill a Mockingbird, there are three instances of Aunt Alexandra's anger:

1. She becomes upset when Jem reveals that he knows about his cousin Joshua who "went round the bend at the University." She is discontent that Atticus has revealed the "skeletons in the Finch closet; so she has Atticus impress upon the children that they are not from "run-of-the-mill people." (Ch.13)


2. She becomes irked by Atticus's speaking about Mr. Underwood's dislike of blacks before Calpurnia. When Atticus says, "He despises Negroes, won't have one near him," Aunt Alexandra frowns at Atticus. After Calpurnia leaves the room, Alexandra says, "Don't talk like that in front of them." (Ch. 16)


3. She is angered by Mrs. Merriweather's insensitive remarks at the Missionary Tea, and then Atticus enters the house to ask Calpurnia to accompany him to the Robinsons' home. Aunt Alexandra asks what has happened and Atticus reports that Tom has been shot as he tried to escape from Enfield Prison Farm. After Atticus departs, Aunt Alexandra is very disturbed by what the town is doing to her brother: "It tears him to pieces. He doesn't show it much, but it tears him to pieces." She resents that the townspeople have Atticus do what they are too afraid to do themselves; namely, insist upon justice. (Ch. 24)