What strikes me upon reading the story is the word choices the author uses to convey the sense of freedom/repression in the story. It is not the physical aspect of her life that deprives her of freedom. In fact, it seems her life was a relatively "easy" one in that sense, one which contains "a comfortable, roomy armchair" for her to sink into. And yet, her emotional state is more like a prison. She is "pressed down by a physical exhaustion that haunted her body and seemed to reach into her soul." Her body is not in jail, but her soul, it seems, is.
By contrast, outside the house (and life) that imprisons her, the world is filled with signs of freedom: "trees that were all aquiver with the new spring life ... The delicious breath of rain..."
in the air. Even the peddler in the street below was freer than Mrs. Mallard. But she could hear freedom: "The notes of a distant song which some one was singing reached her faintly, and countless sparrows were twittering in the eaves." One gets the sense that she wishes she could join them.
Her lack of freedom shows in her "fair, calm face, whose lines bespoke repression." She is weighed down by her life, until she realizes that she now faces "a long procession of years to come that would belong to her absolutely."
She seems to have been well acquainted with the "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." It is that will which steals her freedom, and the loss of the embodiment of that will--her husband--which gives her back that freedom (if, indeed, she has ever really experienced freedom before).
All of these phrases convey the strong impression of the emotional prison which stifles her, and the tantalizing new life which she sees unfolding before her, at the death of her husband.
I hope this helps get you started!