This short story takes its title from the standard legal phrase, but the term "peers" lies at the base of the question. In this era, when women were not considered "peers" of men, but were considered lower-class citizens, the men (sheriff, etc.) are not peers, but the women are (and it is important that one of the women is the sheriff's wife), and the women have "judged" her to be innocent by reason of self-defense. Finding the bird with the broken neck, the women piece together what has happened, and as her peers have found her innocent, while the "law" might not. That is the social statement that Susan Glaspell is making here and in the play the short story is adapted from, Trifles.