Miss Strangeworth notices that many people in the town seem disturbed, but she does not realize that her poison-pen letters are responsible for much of this disturbance. One of the earliest examples of a character who seems disturbed is Mr. Lewis the grocer.
Mr. Lewis looked worried, she thought, and for a minute she hesitated, but then she decided that he surely could not be worried over the strawberries. He looked very tired indeed....
Presumably the grocer has been the recipient of one or more of the old lady's poison-pen letters, although the reader is never informed of the message or theme. Mrs. Strangeworth also runs into Adela Harper at the grocery store.
Her hand shook slightly as she opened her pocketbook. Miss Strangeworth wondered, glancing at her quickly, if she had been taking proper care of herself. Martha Harper was not as young as she used to be, Miss Strangeworth thought.
We learn later in the story that Martha Harper must have received at least one of Miss Strangeworth's letters, and the letter the sweet, vicious old lady composes that day shows us the kind of fear and worry she is implanting in Mrs. Harper's mind. In her new letter, Miss Strangeworth writes:
Have you found out yet what they were all laughing about after you left the bridge club on Thursday? Or is the wife really the last one to know?
Obviously, Miss Harper is disturbed about at least three things. One is that her husband may be having an affair. Another is that everybody in town seems to know about it except her. And in addition, she is now suspicious of many of the women she knows, wondering which of them might be having an affair with her husband.
Miss Strangeworth has made Linda Stewart and her boyfriend Dave Harris very unhappy by writing one or more of her poison-pen letters to Linda's parents, suggesting that Linda and Dave, who are young teenagers, may be engaging in illicit sex. Linda's parents, of course, are also very disturbed and are doing their best to separate the teenagers, who are truly in love.
Judging from her output on the day of the story, Miss Strangeworth is sending out several letters just about every day. This is having the effect of making most of the people in town unhappy and paranoid. Ironically, Miss Strangeworth is aware that "many people seemed disturbed recently," but she has no idea that this is due to her letter-writing.
The ironic thing about these letters is that they could be interpreted as intended to be helpful. There are many people like Miss Strangeworth, but they don't write poison-pen letters--as far as we know.