How was Mrs. Dubose acting in Chapter 11?

In Chapter Eleven, Mrs. Dubose is very rude to the children. She is known for being a very mean, sick old lady who sits on her front porch and yells insults at Jem and Scout as they pass by, but he day after Jem's twelfth birthday, when he and Scout went to town to spend some of his birthday money, Mrs. Dubose yells at Jem. She accuses him of breaking Miss Maudie's grape arbor, she yells at Scout for wearing overalls, and then she starts yelling at them about how Atticus is defending "niggers," saying that Atticus is no better than "the trash he works for."