In Eudora Welty's story, "Why I Live at the P.O.," the narrator has a very clear and strong voice. The narrator, Sister, is sassy and opinionated--she has a thought on just about any topic and is always ready to share it. She feels victimized by her family and when her sister, Stella-Rondo, comes back home, pregnant, stealing the limelight, Sister is not happy. Sister becomes sarcastic and petty to every member of her family. She is the classic unreliable narrator because her attitude makes it difficult to know what is the truth and what is an exaggeration.
It's always difficult to say whether a narrator and author are the same, or if they share the same voice, and really, readers should not make the assumption that this is so. Even though any narrator or character may have a small piece of the author in them, that isn't to say that they have the same voice. In this case, Sister seems quite the opposite of how everyone knew the author, Eudora Welty, to be. Those who knew Miss Welty said she was a soft-spoken, gentle, southern woman. It seems unlikely that she would have ever talked or sounded like Sister in this story.