In what ways was Mrs. Mallard's reaction different or unusual after she heard the news of her husband's death?

Mrs. Mallard's reaction to the news of her husband's death is that of a woman freed from a long prison term.  She is shocked into silent disbelief, overcome with emotion, struck with a sense of relief at being free from the burden of marriage.  She is now a widow who will be accepted in society, free to make choices, to have friends, to attend social events, to decide each day what she will do, according to what she wants.  No more bending to the will of a husband, whom she loved most of the time.

Mrs. Mallard's reaction is not the typical hysteria, crying and grieving of a wife who has lost her husband, the man she loves. Louise Mallard sits in her room, staring out the window, imaging the life she will now have, free to choose, to explore her likes and dislikes.

Mrs. Mallard lives a lifetime in the space of one hour as she imagines what she will do with all her new freedom.  She journeys in her mind, wandering free to enjoy and appreciate the life she sees through her window. 

Sadly, her new life is brief, cut short by the abrupt return of Mr. Mallard, who was not anywhere near the train accident.  His poor wife, so overcome by his return, along with her bad heart, is so stricken, that she dies right there on the spot.  Mrs. Mallard's heart gave out, she was unable to bear the thought of living under the control of her husband, not after she imagined the life she could have alone.