Answer:
Mrs. Mallard's excitement at the prospect of a new life.
Step-by-step explanation:
The narrator tells us that, when Mrs. Mallard went to her room, she saw the tops of the trees which were all aquiver with the new spring. This spring is a symbol that represents the newfound liberty of Mrs. Mallard. It also conveys her excitement at the prospect of a new life, now that her husband has died and she has become independent.