What situation has prompted the narrator to tell the story? What does the story from this narrator tell you about her daughter Dee? About Maggie? How does help to establish the theme?

The narrator has been prompted to tell this story by the impending visit of her daughter, Dee, who moved away for school and, apparently, has been somewhat estranged from her mother and sister since that time. Mrs. Johnson considers her reunion with Dee, dreaming of the reunions of children and their parents she has seen on television; the child has "'made it'" and is "pleasant[ly] surprise[d]" by the sight of her parents, who totter "in weakly from backstage." Mrs. Johnson knows that this kind of reunion is not to be: she is not weak or tottering, and Dee is not the kind of daughter to tearfully pin an orchid to her mother's dress. Mrs. Johnson and her other daughter, Maggie, are preparing for Dee's visit, and both seem to be a little apprehensive, to say the least, about her arrival. This prompts Mrs. Johnson to narrate her story.
Mrs. Johnson tells us that Dee "would always look anyone in the eye. Hesitation was no part of her nature." Dee had hated their first house, and she might have "hated Maggie, too." Mrs. Johnson describes how Dee would "read to [them] without pity," seemingly purposefully making them feel stupid. Dee is materialistic, always "want[ing] nice things," and Mrs. Johnson describes Dee's humor as "scalding." Her mere presence seems to burn people, figuratively—to wound them. Even now, the dress she wears when she arrives "throw[s] back the heat of the sun." Her demeanor is off-putting; she wants objects that her mother and sister use every day so that she can "do something artistic" with them in her own home. She does not care about what anyone else wants.
Maggie, on the other hand, is the reverse. She obviously loves her mother, just as she's clearly sort of intimidated by her sister. Just as Dee is used to getting what she wants, Maggie is used to giving way. When Dee demands the family quilts that had been promised to Maggie, Maggie says,

"She can have them, Mama," [. . .] like somebody used to never winning anything, or having anything reserved for her. "I can 'member Grandma Dee without the quilts." [...] She looked at her sister with something like fear but she wasn't mad at her. This was Maggie's portion. This was the way she knew God to work.

The fact that Maggie values her memories of her grandmother more than the quilts themselves shows that she and Dee have a completely different understanding of heritage. For Dee, it is something to be preserved, shown off, hung on the wall: it is contained in objects. For Maggie, it is something lived in the present, something kept alive: it is contained in memories and practices and story-telling. These differences in the two sisters' views conveys one of the story's major themes: that heritage is not necessarily about retaining objects but about retaining memories and traditions that give value and meaning to one's life.