Answer:
When she realizes that she is finally free, silently exclaiming under her breath "free, free, free!" shows the moment she had a change of heart.
Step-by-step explanation:
Mrs. Mallard at first seems taken aback and shocked to hear of her husband's death from her sister. But after a while, that feeling of grief changes to something that was even unexpected by her. She felt a sense of freedom and release from a controlling, dominant hand that he used to exert over her during their times together. The first indication of this change in the reaction is evident in the lines "She said it over and over under her breath: "free, free, free!", suggestive of the fact that she feels free and finally able to be rid of his "powerful will bending hers".