Dee has gone out into the world and become successful. We don't exactly know what all she has succeeded at, but we do know she has had a very good education that her mother has paid for at great expense to herself. Whenever Dee comes home she seems to be quite prideful and remind her mother and sister how uneducated they both are. Her mother, in spite of paying for Dee's schooling, never got past the 2nd grade herself.
One would hope that Dee would be grateful for the sacrifices her mother has made to provide such good opportunities for her, but instead Dee looks down on her poor, uneducated mother and sister. She does not see herself as one of them. Rather, she sees herself as successful and that they are not. She sees herself as cultured and that they are not.