Mama is practical, a pragmatist. She understands, on some level, that Dee/Wangero is interested in her heritage and their family's place within that context; that, in and of itself, isn't necessarily a bad thing. Dee/Wangero's track record, however, suggests that she's apt to change--her interest in Black American heritage and its embodiment in the quilts could simply be the proverbial "flavor of the month." To Mama, the quilts possess far more value in their being used--something Maggie is far more likely to do. Her younger daughter may not be "book smart," but she will live a life that will make use of the quilts as quilts, not as signifiers.
she feels that Dee is going through a phase and if she gives her the quilts she would showcase them in her house, and when the fad is over she would toss it away as if it was nothing.