In The Open Window, what actions on the part of Mrs. Sappleton show that she stands in the "nice division"?
Mrs. Sappleton is a friend of Frampton Nuttle's sister. She does not know Mr. Nuttle at all, but Frampton's sister has sent her brother to meet Mrs. Sappleton while he is in the country recovering from some sort of mental breakdown. Framptom basically shows up uninvited while Mrs. Sappleton is expecting her husband and brothers to return from a hunting trip. She makes small talk and politely listens to him babble on and on about his "ailments," something that would bore anyone in her position, so you can assume that she is nice because she does not send him away.
However, even though Mrs. Sappleton really has no need to be entertaining a stanger, she is expected to so by people in her social circle at this time in history. Her behavior, therefore, does not ncessarily mean that she is nice but rather than she follows the prescribed etiquette of her time.