The speaker of "Immature girl" feels lost, and she says so in the plainest terms. She calls herself a random girl, a failed teenager, a mess. The words are blunt and a little harsh, as if she has already decided what she thinks of herself and isn't looking for comfort. What troubles her most is that she can't find "the old me." She doesn't describe a self that slowly changed. She says she erased it, which puts the blame on herself.
The poem's shape follows her feeling of shrinking. It begins with her wandering in her own thoughts and ends with "emptiness and dark." The short lines and simple wording make it sound like a quiet confession rather than a dramatic outcry. The mood is heavy, lonely and self-critical, though the honesty of the poem hints that part of her still wants to understand what happened.