Quote 1
When she abandoned herself a little whispered word escaped her slightly parted lips. She said it over and over under her breath: "free, free, free!" (11)
The idea of being "free" has to escape from Mrs. Mallard. It's not as though she readily admits it or eagerly shouts it out. She barely opens her mouth and barely raises her voice. The word "free," itself described as tiny, has to sneak out of her.
Quote 2
"Free! Body and soul free!" she kept whispering. (16)
Significantly, the emotions Mrs. Mallard feels in this moment are powerful and strong. This can be seen in the repeated use of exclamation points, the repeated emphasis on the idea of "freedom," and the combination of her entire body and soul being caught up in this feeling. However, it seems like the feelings are almost too strong to be expressed. Mrs. Mallard can only "whisper" them.
Quote 3
She was beginning to recognize this thing that was approaching to possess her, and she was striving to beat it back with her will – as powerless as her two white slender hands would have been.
When she abandoned herself a little whispered word escaped her slightly parted lips. She said it over and over under her breath: "free, free, free!" (10-11)
Weirdly, the concept of freedom seems to take over Mrs. Mallard's body. She's "powerless" to stop the feeling of freedom from "possess[ing] her," even though the idea of freedom traditionally seems to indicate choice and personal authority. Here in order to be free, Mrs. Mallard can't be free from her idea of freedom.