The sky symbolizes freedom safety and opportunities. Esperanza tells us that on mango street there's too much sadness and not enough freedom, safety, and opportunities. she also tells us she is going to shake the sky, like she is going to get out of mango street and have freedom, & much more.
And as shown in the story it claims that.. "Esperanza in the rising, the sky represents her potential to soar the high sky and realize her dreams.
Therefore the sky helps her accomplish her dreams.