When Francis talks to Scout he reveals an unpleasant feature of Aunt Alexandra. What is this?
In chapter 9, the Finch family gets together to celebrate Christmas, and Scout is forced to spend time with her boring, antagonistic cousin, Francis Baker. After dinner, Scout and Francis go outside, and Francis begins criticizing Atticus for defending a black man and not raising his children properly. Francis repeats Aunt Alexandra's derogatory comments, which reveal that she is a racist. Francis tells Scout,
"Grandma [Aunt Alexandra] says it’s bad enough he lets you all run wild, but now he’s turned out a nigger-lover we’ll never be able to walk the streets of Maycomb agin. He’s ruinin’ the family, that’s what he’s doin’" (Lee, 85).
Aunt Alexandra clearly does not support her brother's defense of Tom Robinson and is ashamed that he is willing to defend a black man. Alexandra's racist comments indicate that she subscribes to the prejudiced ideologies of Maycomb's community. Later in the novel, Aunt Alexandra expresses her concerns about Atticus defending Tom Robinson but sympathizes with Atticus. She witnesses firsthand how the trial negatively affects Atticus and wishes that he would simply not defend Tom Robinson.
I assume that you are talking about what Francis says to Scout in Chapter 9 when the clan is all at Finch's Landing. The things Francis says to Scout while he is making fun of her make it quite clear that his grandmother (Scout's Aunt Alexandra) is racist and also very arrogant and stuck up.
Francis tells Scout about Alexandra's attitude towards Dill. She clearly looks down on Dill because of his family situation. She compares him to a stray dog. Aunt Alexandra has also, apparently, been saying what they thought was bad things about her brother Atticus. She has told Francis that Atticus is a "nigger-lover."
By saying those things to Francis, she has shown that she thinks she is better than others because of her family background and she has shown that she is racist.
She is found out to be a racist woman and this is understood when Francis explains that she looks at Dill like a stray dog and she also believes she is high and mightier than people who are of color. This is also demonstrated when she tells Atticus to let Calpurnia leave but he would not have this.