After leaving home, Dee spent time researching her African ancestry and decided that she could no longer bear being named after her "oppressors." This statement greatly troubles her mother, who reminds Dee that she was named not after any oppressors but after Mama's sister, Dicie, whom they called "Big Dee" after Dee is born.
Dee rejects this explanation, pressing her mother to explain whom Big Dee was named after. When Mama counters that Big Dee was named after Grandma Dee, Dee again challenges her. Once more, she asks whom Grandma Dee was named after. Mama retorts that Grandma Dee was named after her mother, but that she could not trace the line of Dees any further than that; she also silently considers how she could likely trace the name all the way back through the Civil War.
Dee carries the name of many women in her family, but instead of seeing this as a gift of ancestral heritage, she rejects it as a sign of her family's oppression, changing her name to Wangero Leewanika Kemanjo.
It is interesting, then, that Dee wants to claim her family's quilt, which contains little bits of her family's history, all the way back to a piece taken from Great Grandpa Ezra's uniform that he wore in the Civil War. Though this tangible fabric seems to hold great meaning for Dee, her name, which carries the heritage of a line of women in her family, does not.
Dee wants to separate herself from those parts of her heritage which she believes shows the oppression in her family's history, which is why she changes her name.