In the excerpt from "The Open Window," the room provides clues about the nature of Mrs. Sappleton and her household. Based on the context and the interaction between Framton Nuttel and the niece, the most accurate assumption he makes is:
He assumes Mrs. Sappleton must either be married or widowed.
Framton's understanding of the social dynamics within the setting, particularly as it pertains to women of that time, leads him to infer the status of Mrs. Sappleton based on the fact that she likely occupies the role of a woman managing a household, a common assumption in the era depicted in the story.