Who might the female narrator in the introduction represent and what function does she serve?

The introduction of My Ántonia is called a frame, or framing device. It is a preface for the novel, and it is written in a voice other than the one that narrates the body of the text. It is called a frame because it provides a very specific context for the novel itself, and it forces the reader to see the novel from a certain perspective. Because it is written in the voice of an anonymous, relatively insignificant character, it creates a distance between the reader and what he is about to read. In creating the folder labeled "My Ántonia," Jim was writing primarily to himself, not to a larger audience. My Ántonia is like a private love letter to this Bohemian girl, and we therefore don't really know anything about Jim Burden. We are intruding on his private correspondence and seeing Ántonia through his eyes, but we don't have any real connection to him. My Ántonia thus becomes the story of Ántonia, not of Jim. She is the central figure of the novel and the person we are supposed to admire as much as Jim does.