In "Smokes Last," what is the rhetorical function of the grilled cheese burning?

A lack of satisfying, nutritious food is a repeated motif in this story. David has to steal bread from a friend's house for the grilled cheese that his mother has promised him, and he forgoes the opportunity to eat at the powwow because his mother says he should come home for lunch. But when he does, she inattentively burns the grilled cheese and blames David for the accident, leaving him to eat a burned sandwich alone while she goes into town. This incident makes a symbolic point about her capacities as a parent.