In her self-created outlook on life, Dee believes that she needs to reject all of her old family life in order to fit in and be accepted by modern society. She even changes her name, if only symbolically, to an African name to better reflect what she believes to be her "true" heritage; in typical shallow fashion, she doesn't understand that she was born far after African Americans were named by their owners.
"I couldn't bear it any longer, being named after the people who oppress me."
"You know as well as me you was named after your aunt Dicie," I said. Dicie is my sister. She named Dee. We called her "Big Dee" after Dee was born.
(Walker, "Everyday Use," xroads.virginia.edu)
Because she can't bear to be proved wrong, Dee insists on asking the full history of the name; when Mrs. Johnson forgets who came before, Dee acts as if this is proof that she was actually named after a slaveowner. Instead, she is just obsessed with being seen as modern and progressive, and doesn't understand that her true heritage is the family life that raised and supported her, allowing her the personal freedom to create her own individual personality. Even though her individual personality is selfish and uptight, it is her own, and she owes the ability to live it to her family and their heritage.