Marianne Dashwood doesn't have much sense or sensibility. She is quick to fall in love and is a drama queen. She is in fact rather manic with her emotions. Until the end of the story, she is driven purely by emotion. Elinor Dashwood is the opposite. She is practical and able to separate herself from matters of the heart and common sense. Unlike her sister, Elinor doesn't pine for a man to "complete" her. Marianne can't keep away from her man and gives over her lock of hair to Willoughby (kind of like a promise ring?) which Elinor finds disturbing. Certainly Elinor fits the definition sense and Marianne embodies "sensibility". We have to understand that in Austin's time the word "sensibility" had a meaning closer to "sensitivity". Marianne operated through emotion rather than practicality.