The Snow White allegory
Snow White's allegory is presented as an ideal version of female life, and the poet is arguing that it isn't fair that some girls get to have their fairy tale while others are left in the mud on the side of the road. The poem is about envy and resent toward the image of the happy princess.
The motif of shamelessness
Snow White gets shade thrown her way by this poet. The poet practically spits on Snow White who is so perfect and so holy and so pure, and the poet can't stand it. She represents all the shame the poet is carrying. All the poet's attentions to shameless imagery (whiteness/purity) is an indication that she herself feels unworthy and unloved.
The motif of insatiability
There's a jarring line in poem about penises wanting openings. That is one of a collection of images representing insatiability, when even getting what one's wants most is not enough to make them stop wanting. She's caught in a spiral of desire, jealous for other people's lives. She feels unsubstantiated and insatiable.
The allegory of the shadow
The treatment of shadow is very interesting in the poem. Instead of the poet representing her own shadow, she feels like a shadow under Snow White's feet, a silhouette of a person. This sense of identity crisis might be fueling the comparison between her life and Snow White's.
The allegory of sibling rivalry
This poem is not unique in its treatment of "me versus him/her." The problem of comparison is treated all throughout literature, perhaps most importantly in the story of Cain and Abel. When Abel accomplishes a great, honorable life, like Snow White represents here, Cain kills him, and the poem represents the resent real people feel toward people who look like they have everything together.