Symbolism, Imagery, Allegory
The wind is Waverly's invisible buddy, teaching her to be strong and sneaky while knocking her opponents over like empty cups in a strong breeze. Okay, actually it's Waverly's mom who tells her "Strongest wind cannot be seen" (2), but still, the wind definitely serves her well. In fact, we might even say that Waverly turns to the wind for strength instead of seeking her mother out directly—leaning on a piece of maternal wisdom despite not feeling like she can openly need her mother's support.
Waverly calls on the wind to help her win her first chess game, since "It whispered secrets only I could hear" (38). And later, when Waverly's all alone in her room, the wind comes along and "pushe[s] [her] up toward the night sky" (69), setting her free.
In a childhood devoid of playmates, the wind is kind of Waverly's best friend, which is a little sad since it's invisible, it speaks to her in whispers, and it can't play with her or hug her or do anything. When your only friend is a force of nature, your life is pretty darn lonely.