How does the conversation between Lizabeth's parents motivate Lizabeth's later actions?

Lizzie's parents' conversation frightens her. Her father's tears not only frighten her.... they shake her world. Her father's helplessness is contagious..... her world has changed, and her anger leads her to ruin Miss Lottie's flowers in response to her own hopelessness.

At first I heard no words, only voices. My mother’s voice was like a cool, dark room in summer—peaceful, soothing, quiet. I loved to listen to it; it made things seem all right somehow. But my father’s voice cut through hers, shattering the peace.

The world had lost its boundary lines. My mother, who was small and soft, was now the strength of the family; my father, who was the rock on which the family had been built, was sobbing like the tiniest child. Everything was suddenly out of tune, like a broken accordion.