Resent, bitterness, and frustration
The primary emotional meaning of the poem is that a girl is remembering the purity and poise of the Disney princess Snow White, and she ends up hating the princess that she loved as a child. She feels this way because her faulty expectations left her with disappointment, confusion, shame and regret when she learned that in real life, none of us get to be "white and pure," as Snow White was.
Whiteness versus goodness
The speaker resents the implication that pure and white is necessarily better than reality and experience. By thinking in terms of idealism, the girl ends up hating the ideal, frustrated by the neverending challenges of real life. There is an implied feminist critique of purity culture and princess culture in young girl's lives.
The curse of human experience
One way of interpreting the fact that Snow White's whiteness offends the poet is to say that the poet feels there isn't justice between the fairy tale life that was shown to her through art and the actual demands of real human life. The question is to what extent the poet will allow her dirtiness to corrupt her character.
