Because going back a bit in the story we see that ''she heard her father crying because he couldn't provide for the family and this made her realize that adults were also vulnerable
it also made her angry and this is why she destroyed Miss Lottie's flowers
when she finished she saw Miss Lottie looked up and saw Miss Lottie and how devasted she was that her flowers had been destroyed
she linked her father's crying and Miss lottie's upset and suddenly feels sorry for Miss Lottie and has started looking at things with an adult rather than a childish/teenage view In this way, we realize that Lizabeth is on the verge of becoming an adult.
