What instances of repetition can be found in "The Story of an Hour"? What is the significance of this repetition?

Much of the repetition of words or phrases in the story serves to reinforce Louise Mallard's sense of her new freedom.

The word "open" is used multiple times: the window in Louise's bedroom is "open," and the square which it overlooks is "open" too.  The narrator describes the way in which Louise imagines her life after her husband's funeral, and "beyond that bitter moment [was] a long procession of years to come that would belong to her absolutely.  And she opened and spread her arms out to them in welcome."  This line certainly connects the repetition of the word "open" to Louise's joy and new independence.  Suddenly, there are so many possibilities for Louise whereas when her husband was alive, she felt that there were not.  The narrator tells us that the lines her in face "bespoke repression," but there is nothing to repress her now.  Her future is wide "open."

Louise herself also repeats the word "free" three times initially, and then later, she says, "'Free!  Body and soul free!'"  Her repetition of these words tells us exactly what she's thinking as she looks out the window at all the signs of new spring life around her.  She is reveling in the seemingly limitless possibilities her life holds now that it is untethered from her husband.

Just before she opened the door to go back downstairs, "She breathed a quick prayer that life might be long.  It was only yesterday she had thought with a shudder that life might be long."  The repetition of the phrase "that life might be long" emphasizes how it used to be such a frightening prospect when she lacked freedom and autonomy and how quickly it has become a desired wish now that she has them.

Taken together, the story's repetition emphasizes Louise's joy at her newfound freedom and all the possibilities she sees for her future now that she believes that she, alone, will determine its direction.  Ironically, the doctors said she was killed by her joy at seeing her supposedly-dead husband walk through the door; in reality it was the too-fast termination of her joy that stopped her heart.