You might consider making the claim that Mrs. Mallard is a character with whom Chopin wants readers to sympathize, despite the fact that she seems to rejoice when she learns that her loving husband has died.
It seems, on the surface, that Mrs. Mallard's apparent joy is, indeed, monstrous, but an examination of the details that motivate her happiness helps us to understand it in context. Published, in 1894, this story depicts marriage as it was at the time: a required institution for every young lady to enter, however much she may fear the loss of her individual identity or the repression of her own will. Mrs. Mallard seems to be a young woman who might have chosen not to marry, had that option been a socially-acceptable one. Once alone, she whispers the word, "'free, free, free!" as though she cannot believe that she now is. The narrator tells us that she's thinking how
There would be no one to live for her during those coming years; she would live for herself. There would be no powerful will bending hers in that blind persistence with which men and women believe they have a right to impose a private will upon a fellow-creature. A kind intention or a cruel intention made the act seem no less a crime as she looked upon it in that brief moment of illumination.
Even though her husband had been "kind, tender," he had still been her husband, and that had given him a legal right to make any decisions for her. The fact that he "never looked save with love upon her" does not change the fact that her will was not her own while he was living. "What could love," she thinks, "the unsolved mystery, count for in the face of this possession of self-assertion which she suddenly recognized as the strongest impulse of her being!" With his death, she is now free to be autonomous; she possesses her own self now and is possessed by no one else. She can now recognize that this autonomy is actually the most important thing to her.
Thus, even though we might typically consider a widow's joy upon her loving husband's death a terrible thing, it becomes a great deal more understandable when we realize that his death actually grants her a new life.