There are many kinds of feminist theories, and there are many ways to apply those theories to Lucille Clifton's poem "There is a girl inside."
When I first had to read this poem in school, I assumed it was about childbirth. The title made me think it was about having a baby. Then something happened: I actually read it.
While this poem isn't about childbirth, you could argue that it's about a different kind of birth: the birth or liberation of a kind of wildness and chaos.
Several feminists advocate that women can embrace their wildness, even though that wildness is sometimes turned against them by misogynists. For instance, Julia Kristeva, a French philosopher, believes women can harness the alleged tumult of the female body and use it to undercut patriarchal ideas. Her theory involves a kind of transformation. She turns a negative sexist trope—that women and their bodies possess a lack of control or organization—into a positive one. Why not use that force to force society to be less parochial and misogynist?
We see similarities to Kristeva when Clifton describes the "girl inside" as "randy as a wolf" and waiting to "break through gray hairs." As with Kristeva, Clifton seems prepared to engage in a kind of benevolent destruction.
To Clifton’s poem, I might also apply Judith Butler's theory that gender is a performance. Butler says that people identify gender based on gestures, looks, and acts. We might think someone is a girl by how they walk, by what they wear, or by what they say. Gender is like a character in a movie, TV show, or play.
How is the girl in Clifton's poem reinforcing that performance theory? How is she performing a "girl" character? Think about all of the nature imagery: the green tree, the woods, the honey, and the thyme. These might reinforce typical representations or performances of girls as particularly connected with fertility and nature, but Clifton's girl doesn't seem disempowered by it. As with the female body/chaos stereotype, perhaps the girl/nature stereotype can be utilized in a pro-feminist way.