What is the purpose of the letters that Miss Strangeworth sends in "The Possibility of Evil"?

It would appear that Miss Strangeworth does not understand her own motive or motives for writing her anonymous letters. She rationalizes that it is her civic duty to keep the citizens of her town alerted to the possibilities of evil threatening them personally. She is the last surviving member of the town's founding family and is exceptionally proud of that distinction—although it means little to anybody else. She is just a lonely old maid who has nothing to do with her time and has to make up activities to fill her days. A good example of this is the way she goes grocery-shopping practically every day and buys in very small quantities so that she will have to keep coming back and have at least one thing to do. She thinks she is so important as a person and as a customer that the store-owner Mr. Lewis should remember that she always buys a small quantity of tea on Tuesdays.

"Imagine your forgetting that I always buy my tea on Tuesday," Miss Strangeworth said gently. "A quarter pound of tea, please, Mr. Lewis."

There is no reason why she couldn't buy a full pound of tea once a month, but this gives her an excuse to keep coming back. Time weighs heavily on her hands. She has only discovered the pleasure of writing her poison-pen letters in the past year. They give her something to do, and she can tell herself that she is contributing to the welfare of the community. She cannot realize that she is a busybody and a troublemaker. Her letters are doing no good, only harm. Much of the evil she suspects in others is a projection of the evil inside herself. This is reminiscent of the biblical injunction:

1 Judge not, that ye be not judged.

2 For with what judgment ye judge, ye shall be judged: and with what measure ye mete, it shall be measured to you again.

3 And why beholdest thou the mote that is in thy brother's eye, but considerest not the beam that is in thine own eye?

4 Or how wilt thou say to thy brother, Let me pull out the mote out of thine eye; and, behold, a beam is in thine own eye?

5 Thou hypocrite, first cast out the beam out of thine own eye; and then shalt thou see clearly to cast out the mote out of thy brother's eye.

                                      Matthew 7:1-5 King James Version

So the alleged purpose of the letters is to guard the morals of her neighbors, while the real purpose is to give Miss Strangeworth something to do and to make her feel important. Why are the letters anonymous? Perhaps she senses somewhere deep in her unconscious that she is causing harm and that she could get in serious trouble for making what amount to false accusations. She can be more creative if her identity as the author is unknown. It is only by accident that her identity becomes known to one person, Don Crane, because she dropped his pink letter accidentally at the post office. But Don Crane probably will not tell anybody except his wife Helen who sent him that letter. He can't tell other people because then people will know who chopped up the old lady's rose bushes. Her secret is still safe for a while.