Personally, I feel like I am always criticising and analyzing Stella-Rondo throughout Why I Live at the P.O. Given that narrator, Sister, is the speaker presenting the story, I found myself instantly taking her side. The constant quarreling, while only explained through the narrator, seemed to lead me to have the same feelings about her sister as she did.
The fact that Stella-Rondo married a man who Sister dated really put me off in the first place. This fact alone forced me to instantly side with Sister.
Therefore, throughout the text, I am constantly on the side of Sister (as I am sure Welty wished of her readers). The story of Sister and her fights with Stella-Rondo are surely meant to appeal to the reader's sympathy for the narrator. Without the narrative voice belonging to Sister, one may not feel as negatively towards Stella-Rondo. Instead, one may rely on their own interpretations of each of the characters and not the emotional pull of Sister's story.