While there are different approaches to the superb story of Kate Chopin, one approach that the writer can take is to examine the tremendous consequences of the patriarchal society in which Mrs. Mallard exists. For, the effect that this repressive society has upon her psyche is an overriding theme in the narrative. In fact, in the opening sentence, the narrator states that Mrs. Mallard demonstrates symptoms of heart problems; however, after the news of her husband's death, she realizes a new-found freedom, and she feels great, "a goddess of Victory." It is only when her hopes and desire of individual freedom are crushed by the reappearance of her husband that Louise Mallard dies of heart failure in "a joy that kills."
If the idea of cultural repression appeals to the writer, she can use a cause/effect method to compose the essay. The thesis, then, will need to establish this cause and effect. Perhaps, it can be worded to demonstrate that as a woman trapped in a repressive society, Mrs. Mallard at first struggles to realize her new freedom, but, then, after reconciling this inner conflct, she is again faced with renewed repression by the reestablishment of subjugation to her husband and society.
There is included in the links below one from an interesting discussion that addresses the same issue as this question.