Why is Mrs. Mallard happy when she thinks her husband is dead?
In traditional Kate Chopin style, "The Story of an Hour" tells the tale of a woman whose submission to social expectations has rendered her lost inside a loveless and boring marriage. Far from any chance of realizing herself, mentally and independently, Mrs. Mallard belongs to a generation of women who had very little choices as far as the roles that they could fulfill throughout their lives. Hence, the very limited options of marriage and motherhood were the only choices for women like Mrs. Mallard to take as goals in life.
However, we find that the character of Mrs. Mallard is far beyond her time and place, for she feels the inkling that life must have something else to offer. Therefore, when she is told that her husband is suspected to be dead, she begins to experience these emotions of joy, freedom, and victory... for the very first time.
She arose at length and opened the door to her sister's importunities. There was a feverish triumph in her eyes, and she carried herself unwittingly like a goddess of Victory. She clasped her sister's waist, and together they descended the stairs. Richards stood waiting for them at the bottom.
So impressed she is to realize the feelings that have been lurking within, that she needs the time to be alone and analyze them.
And yet she had loved him--sometimes. Often she had not. What did it matter! What could love, the unsolved mystery, count for in the face of this possession of self-assertion [..]!
"Free! Body and soul free!" she kept whispering.
This shows us the reason why Mrs. Mallard is happy after hearing the news of her husband's death: she thinks that she has finally found a way out of a lifestyle that does not fit her any longer. This reminds us of another famous Kate Chopin character, Edna Pontellier, in The Awakening. Edna also feels that married life and motherhood are simply not for her; and, when she is faced with no other choice, she dies. Therefore, in Chopin's works, women do not refuse to follow the tenets of their generation; for they follow them quite well. It is simply that society has not permitted the women to express themselves in the way that they deserve.
Conclusively, as Mrs. Mallard sees her husband coming back, realizing that he is not dead after all, she dies of a heart attack which is ironically (and erroneously) labeled as "joy that kills." Not true. Mrs. Mallard simply could not believe that all of those emotions of freedom and self-realization would now have to be either denied or returned back to the bottom of her soul. She could not do either of those things. Seeing that life does not fit her mentality any longer, her heart gives up, and Mrs. Mallard dies.
When the doctors came they said she had died of heart disease--of the joy that kills.