What do you think prompted Mama's decision to give the quilts to Maggie instead of Dee?
Mrs. Johnson wants Dee to be the next matriarch in the family. She wants her to be like Big Dee, Grandma Dee, like herself--strong-willed, self-sufficient. Maggie, after the house fire, feels like she has no purpose, no everyday use. Mama wants to give her a purpose, a use, in the quilts. Mama gives her the quilts as a way of acknowledging her past and her pride in her heritage, home, and the "everyday use" of heirlooms.
The quilts are emblems of living history. They are like what other family's might give in terms of inheritances, wills, land, etc... except that quilts tell stories. They are multi-generational; they are the by-products of hard work and sacrifice. The maker of the quilt is not ashamed of her poverty, her slave past. She does not forsake the quilt by hanging it on the way. She honors it by using it and giving it to another who will use it. By this means the quilt remains a quilt, as it is used as it was originally intended to be used.
The same is for culture and heritage. Mama knows Maggie, unlike Dee, will honor the culture and heritage by using it, or continuing it the way it was originally intended. Dee is too mobile, too outspoken, too fickle, too possessive of material objects to be a legitimate matriarch of the family.