While there is no definitive answer, it would seem that Glaspell gave her short story a different title from her play that was published a year earlier in order to distinguish it from this play, first of all. Then, because there are more details in the short story that point to the men's chauvinism as well as Mrs. Hale's staunch defense of Mrs. Wright, Glaspell may have felt "A Jury of Her Peers" a more apt title. For, the allusion is to the rule that an accused man on trial was entitled judged by a jury of his peers, twelve men. Likewise, Mrs. Wright in Glaspell's story is judged by her peers, the sherriff's wife and the neighbor's wife, who find her murder justifiable and hide the evidence, which will show motive, thus preventing her conviction. This scene at the end of the play certainly justifies the title of Glaspell's story.
Mrs. Peters turned her head until her eyes met the eyes of the other woman. There was a moment when they held each other in a steady, burning look in which there was no evasion nor flinching. Then Martha Hale's eyes pointed the way to the basket in which was hidden the thing that would make certain the conviction of the other woman--that woman who was not there and yet who had been there with them all through the hours.
Mrs. Hale and Mrs. Peters have become the "peers" of Mrs. Wright in their subjugation to their husbands' condescending words and manners. So, they become complicit with her by hiding the evidence since these women are all subjective in their judgments, as well.