Why does aunt Alexandra get angry at Atticus?

Why does aunt Alexandra get angry at Atticus?
Alexandra gets angry at Atticus because he said that Braxton despises Negroes in front of Calpurnia.OrThe contrasts are extreme. Scout thinks her aunt finds her dull while she knows Atticus finds her interesting. Alexandra has "river boat boarding school manners," and while Atticus is a gentleman, he is also very relaxed and unpretentious. She feels she is better than others, while Atticus is quick to tell her that their "generation's practically the first in the Finch Family not to marry its cousins," noting they are as "common" as anyone else. Alexandra wants Scout to behave like a lady, and while Atticus tries to reinforce his sister's wishes, Scout knows that he loves her the way she is, which, at the time, is more of a tomboy than a lady.