Your secondary question concerning the reticence of the narrator raises an interesting issue. The mode of narration in this story is first person, and because of this we must be aware that we might not be receiving an entirely reliable narrative - the "unreliable narrator" is a key aspect of first person narration, though perhaps here it is not so unreliable. However it is clear that the speaker is withholding information from both of her daughters, or perhaps, not willing to reveal the whole truth.
When Maggie asks her, "How do I look, Mama?", her mother dodges the question, and then goes on to tell us the readers how Maggie really looks:
Have you ever seen a lame animal, perhaps a dog run over by some careless person rich enough to own a car, sidle up to someone who is ignorant enough to be kind to him? That is the way my Maggie walks.
She does not reveal this "truth" to Maggie, but through the mode of narration we as readers are privileged with this information.
We are also left to infer how the speaker feels about her second daughter, the renamed Miss Wangero. However, it is clear from what she says and does that she disapproves of her and her actions. For example, the narrator buries the argument about the origins of Dee's name, even though, "in fact, I probably could have carried it back beyond the Civil War through the branches." Likewise, it is important to examine the use of words to describe Dee's acquisitiveness. She is described as "rifling" through the trunk, and the narrators meditation over the handle of the dasher, where she is obviously thinking of her family's history and how it has been passed down through the generations.
So the narrator, therefore, refrains from making overt judgements regarding her two daughters, though it is clear that this is often to keep the peace rather than a deliberate attempt to be deceitful.