Given that the story is told through the mother's perspective, we see two very different women through her eyes, and certainly two very different impressions of these women.
Dee is the ambitious, beautiful, popular, and driven daughter. Mrs. Johnson's day dream of meeting Dee on a TV show and having her daughter pin an orchid on her dress (a gesture of thanks and acceptance) show that she both loves her daughter very dearly, and resents her a little. She feels rejected by this daughter for not being "feminine" enough, or "smart" enough, or simply not "enough." But given the way she treats her (allowing her to come home and eat, taking an interest in Dee's new boyfriend, imagining a time when their relationship is mended) it is obvious that the narrator does love her daughter Dee and even takes pride in her intelligence, beauty, and ambition.
On the other hand, Maggie is just as rejected as the narrator. Mrs. Johnson loves her unconditionally, perhaps because no one else does. It seems like Mrs. Johnson and Maggie only have each other. Mrs. Johnson provides the love and protection that this daughter would otherwise never receive. Though her sister Dee has clearly been the dominant personality in the house for years (and likely both mother and sister have allowed it), in the end, the narrator stands up for Maggie by giving her the quilts. This simple act of devotion and protection shows the narrator's unconditional love for Maggie.