Aunt Sally is an example of a respectable citizen, and she is bigoted and not too bright.
Tom Sawyer’s Aunt Sally stands out as one of the crudest of the supposedly good citizens. It is people like her that confuse poor Huck, who wants to follow his conscience when society is telling him something different.
Pretending to be Tom, Huck comes to visit unannounced. He tells Sally that his riverboat “blowed out a cylinder-head.” Her reaction is a perfect example of satire in race relations.
“Good gracious! anybody hurt?”
“No'm. Killed a nigger.”
“Well, it's lucky; because sometimes people do get hurt. (ch 32)
The implication is that a slave is not a person. Sally asks if anyone was hurt, Huck says a nigger was killed (he does say "no"), and Sally says it’s lucky because sometimes people get hurt. To her, a slave is not a person. She has no sympathy for the slave. It doesn’t even register for her. Her reaction is inquisitive relief, not sadness.
Aunt Sally is satirized in other ways. Tom and Huck play a trick on her with the spoons, switching them on her when she tries to count.
But she counted and counted till she got that addled she'd start to count in the basket for a spoon sometimes; and so, three times they come out right, and three times they come out wrong. (ch 37)
The general impression is that Aunt Sally is not too bright. Of course, her thoughts on society just mirror everyone else’s. She thinks what people tell her to think. She accepts what she is told, unlike Huck, and never questions anything. She is just the type of civilized person Huck can't stand to be around, and does not want to become.