In "Rules of the Game", how does Waverly show that she understands the use of strategy even before she starts playing chess?

When Waverly was six years old, her mother did not allow her to have a treat, salted plums, after throwing a temper tantrum for them. The next time Waverly went to the store with her mother, she consciously kept herself from acting inappropriately, so her mother bought a bag of the candies as a reward for Waverly's good behavior. Waverly's awareness of the consequences of her actions is directly related to her grasp of strategy. She not only sees that her actions have inevitable results, but is able to recognize what the results will be.