Further, we can learn more about the main character, Louisa Ellis, and why the title refers to her. It is about a woman who lives in New England and lives alone.  Louisa has made a very happy and solitary life for herself as she waits for her beau, Joe Dagget, to return from Australia after fourteen years.  When he finally returns, the two are awkward and no longer in love.  Further, Joe Dagget has fallen in love with Lily Dyer (who is currently taking care of Joe's mother).  Louisa releases Joe from his engagement.  Now Joe is free to be happy and marry Lily. 

Even though religion isn't necessarily prominent in this story, Louisa has many qualities that befit a nun's life.  She lives in self-afflicted isolation.  She is a woman.  She is a virgin.  She prays every day.  Apart from these general truths about Louisa, there are specific things she does as well that resemble a nun's life.  Louisa is absolutely set in her ways after living without Joe for so long.  She is obsessed with cleanliness.  We know this because Louisa gets mad when Joe tracks dirt all over the floor, puts her books away in different places, and clumsily knocks over her knickknacks. 

In conclusion, the irony is that Louisa is not a nun, but she might as well be.  The simile quoted above which is the last line of the story as well as the similarities to Roman Catholic nuns indicated by Louisa's behavior are the best proof.

In the short story "A New England Nun" by Mary E. Wilkins Freeman, a woman named Louisa Ellis is scheduled to marry Joe Dagget in a week's time. They became engaged fifteen years earlier, but then Joe went off to Australia to make his fortune. Upon his return they have been getting to know each other again but in a formal way. Louisa has become accustomed to her neat, well-ordered life as a single maiden, and she sees Joe's rough ways as an intrusion. However, she and Joe made a promise, and they both feel bound to keep that promise, even though they have little in common anymore.

This all changes when Louisa takes an evening walk and overhears Joe and a woman named Lily Dyer talking. It seems that Joe and Lily love one another, but Joe fully intends to honor his promise to Louisa, and so Lily is planning to go away. The next time Joe visits, Louisa breaks off the engagement. At the end of the story, she feels a deep joy in her maidenly solitude.

According to the Merriam-Webster dictionary, a nun is "a woman belonging to a religious order; especially, one under solemn vows of poverty, chastity, and obedience." Chastity means "abstention from sexual intercourse, purity in conduct and intention, and restraint and simplicity in design or expression." We understand from this definition that Louisa has been living a chaste life.

Louisa is not a literal nun, of course, because she has made no vows to a religious order. Freeman uses the word in a symbolic sense to indicate Louisa's commitment to solitude and desire to live without a man's presence. The title "A New England Nun" carries this symbolism. Louisa has chosen a life of chastity. In this she resembles a religious nun.

In the last paragraph, Freeman emphasizes the symbolism by comparing Louisa's upcoming days to the beads on a rosary, which is something that nuns and other Catholics use to count their prayers. Louisa's solitude and chastity have become so profound to her that they have almost taken on religious significance. The phrase in the last sentence "prayerfully numbering her days" alludes to Freeman's comparing the days with beads on a rosary.

A cloistered nun is a nun who has taken religious vows and has entered a community that is closed off from the outside world. Freeman refers to Louisa as an "uncloistered nun" because Louisa chooses to live like a nun but has not shut herself off completely from the world.