Atticus calls Mrs. Dubose a "great lady" because she has the most courage of any person he has ever known. an example of this is when Atticus explains to Jem how courageous Mrs. Dubose was by quitting her addiction to morphine even though she know she was going to die.

"she said she was going to leave this world beholden to nothing and nobody. Jem, when you're sick as as she was, it's all right to take anything to make it easier, but it wasn't all right for her. She said she meant to break herself of it before she died, and that's what she did."

Mrs. Dubose wanted to "leave this world beholden to nothing and nobody" means that she did not want to feel obligated before she died. She wanted achieve her goal of quitting her addiction to morphine before she died. this shows courage. When Atticus says, " it's all right to take anything to make it easier, but it wasn't all right for her" shows that Mrs. Dubose could have just easily said "I don't care about Quitting my addiction i'm almost dead it dose not matter now" but she quit before she died. This shows courage. overall Mrs. Dubose is a "Great Lady" cause she has courage.