Trifles can be interpreted as a feminist document in that the central theme attempts to defend the main character, Minnie, who was an abused woman in a male-dominated society.
Along with this, this same woman is seen under a petty light by the men in charge of conducting the investigation as to what happened to her husband, who died under strange circumstances that point directly at Minnie.
What makes it a feminist document is also that each of the men conducting the investigation is counteracted by a female character: Mrs. Peters, and Mrs. Hale.
These two are the actual two minds at work who are able to connect all the "trifles" that the men are finding throughout their investigation and realize that Minnie must have snapped at once during one of her husband's abuses, this latter one being a particularly violent one involving him killing her only companion, a canary.
Moreover, the sympathy that the women feel for Minnie is not typical of the thoughts expected of the time, where women were expected to agree with the ideals of males.
Hence, it is a huge step in thematics to see a play in which a woman is clearly guilty of the murder of her husband, and yet such action is almost perceived as a heroic act which has the pardon of her fellow females.