Mrs. Hale and Mrs. Peters are the two key characters in this excellent play by Susan Glaspell as they through their actions and words show an understanding of Minnie Wright's position and, in their discovery of the motive for the crime, act together to ensure that she is not punished for what they consider to be a justifiable murder.
Out of the two characters, it appears that it is Mrs. Peters who is the more timid and the more subservient. It is Mrs. Hale after all who shows in her tone of voice that she is not happy with the men-folk disparaging the role of women and the work that they have to do. Note how she says to the men, "stiffly", "There's a great deal of work to be done on a farm." Mrs. Peters doesn't appear to be a character with enough daring to challenge the men, even in such an implied fashion. Note how she says, when Mrs. Hale begins to finish the sewing, "I don't think we ought to touch things."
Crucial to the play is the fact that Mrs. Hale knew Minnie Wright before she married John Wright, and thus is able to draw the comparison between how she was before, and how John Wright changed her character, for the worse.
Lastly, it is Mrs. Hale who appears to be the more observant out of the two and finds the clues necessary to piece together the motive in the "trifles" that the men so readily dismiss, finding the bird and then putting herself in Minnie Wright's position:
If there'd been years and years of nothing, then a bird to sing to you, it would be awful - still after the bird was still.
Interestingly, in response to this deduction, Mrs. Peters still continues to present the man's view, saying that the crime was "awful" and therefore indicating that Minnie Wright should be punished. However, Mrs. Hale is able to bring her around by describing Minnie Wright's character and the kind of life she would have led under the thumb of John Wright, and in the end they become co-conspirators in hiding the evidence from the men.