At the beginning of the the story she was less mature and much more playful and doesn't realize that her actions have consequences she said her self that she was still childlike enough to go to Mrs. Lottie's house.
Throw the rocks at the marigolds
After seeing her parents fight and her dad being the reserved one rather than her mom she was showing change into adulthood, meaning before doing things like this she will think if it is the right move.
After thrashing Miss Lottie's garden she truly realised what she had done. She had ruined the one thing this woman loved and she could not undo it. She thought "That violent crazy act was the last act of childhood."