In one of the final lines of the story, Phoenix says, "I going to the store and buy my child a little windmill they sells, made out of paper [….] I'll march myself back where he waiting, holding it straight up in this hand" (99). We all remember what those toy windmills look like, right? There's no front or back, no beginning point or end point of a windmill, and when the wind blows, they circle around and around. Maybe you call them pinwheels.
Phoenix's journey is cyclical like the paper windmill. She goes to town for her grandson's medicine, returns home, and then ventures out again the next time the "time come around" (44). A weaker person might throw in the towel and give up. But not Phoenix.
You might be familiar with another literary windmill. Don Quixote famously fights a windmill when he mistakes it for a giant. Thing is, Don Quixote is decidedly out of touch with reality. With this in mind, it seems possible that in having Phoenix buy the paper windmill, Welty is offering up a clue about how in touch Phoenix is with reality as well. Are her efforts to save her grandson in vain perhaps? Is Phoenix somehow being played by the hospital? We don't have an answer, so we'll let you try to sort through this one yourself.