Mrs. Dubose says some harsh things about Jem, Scout and Atticus as the kids pass by her house. She also says nice things about Scout's mother. Mrs. Dubose is cantakerous and rude to an extent that far exceeds normal bounds and her comments are also highly personal.
When she attacks Atticus, she points to his defense of Tom Robinson as a character flaw, though she calls Atticus to her death bed, counting on his good nature for support in her last moments.
Mrs. Dubose is indeed a very grumpy woman. She represents the reaction of the townspeople to threats to the status quo. When Atticus defends Tom, it is a threat to the status quo because most of the townspeople are racist and do not feel that he deserves a trial.
The homeowner is Mrs. Dubose. What she says to the kids is mean stuff about their father and about them. She criticizes the way they are being raised and the way they are behaving. Then she starts in on criticizing Atticus for defending Tom Robinson (because he's black).