The title of this story is ironic because of the pronoun. The only people who can really understand Mrs. Wright's action are women, her peers. However, the only people responsible for doing the investigation and judging are men, who cannot understand the situation.
Mrs. Hale and Mrs. Peters decide to hide evidence that would have shown the men why Mrs. Wright might have killed her husband. They protect her, in other words, and decide to prevent her from being punished.
Mrs. Wright is responsible for killing her husband. She did kill him. However, the question of whether she did murder is up for dispute. Was what she did justifiable homicide? Self-defense? How abusive was Mr. Wright? Can any of us who weren't part of that jury of her peers ever know?