Susan Glaspell's play "Trifles", as well as in the story "A Jury of Her Peers" are based on the same plot: A homemaker named Mrs. Minnie Wright has been held accountable for the death of her husband, John, who dies by hanging in his own bedroom while she sleeps.
It is very hard to justify any kind of action that leads to murder or to hurt anybody. However, the evidence that Mrs. Hale and Mrs. Peters find throughout the Wright household points out that there has been a patter of severe abuse from John to Minnie. As a a result, it is likely that Mrs. Wright has simply snapped after tolerating so many years of harsh treatment.
Among the evidence found at the scene, there is a quilt that has been sewn as if under a fit of hysteria. This is significant because it shows the state of mind of Minnie Wright in her own home: A place where she is supposed to live in peace.
Moreover, there is the evidence that John killed Minnie's sole companion: Her canary. The evidence shows that someone wrings the bird's neck and that Minnie has, at some point, given it some form of respectful "burial" by placing it carefully in the box that the ladies find.
Hence, although no murder is ever justified (since we are supposed to be civilized and not use extreme measures to justify a cause), Minnie's actions are not a result of conspiracy. She has obviously suffered a severe trauma and she is reacting to it in a psychological and not social way. That is how we can come close to justify her actions.