Of course, you want to adhere to any guidelines or expectations that have been given by your professor. Also, take into account the type of assignments you have had so far and what the professor seems to value and appreciate in student work. Consider the objectives of the course. Once you've thought about those--standard procedure for any college assignment you are undertaking--you're ready to brainstorm a bit. Check out the "Girl" summary and study guide on enotes to familiarize yourself with some of the context and features of the piece.
There are definitely some unconventional, defining things about this short story that you'd want to cover in any type of paper or overview. The first aspect has to do with the wording. Kincaid uses colloquial speech rather than formal English. She also writes the entire piece in a single sentence. Now, assuming Kincaid is a savvy writer who knows how and when to end a sentence, we can guess that she has her reasons for making these choices about the text. You could explore the different rationales behind these stylistic choices. For example, the extraordinarily long sentence could communicate what the speaker views as an unending string of commands that she can barely take a breath to complete before another set comes at her.
The other thing to explore is the relationship between the speaker and the voice delivering the commands she recieves. The voice is brashly critical, cruel even, but also instructional. Is the mother figure being harsh on the girl out of jealousy? Fear? Tough love? What might the tone of her voice and the things she's concerned about reflect this family's station in society? What does gender have to do with it? (The title of the piece being "Girl" and the reference to the girl being "bent on becoming a slut" cries out for some feminist attention.) All these questions have diverse answers, but my bet is that your professor is looking for (A) you to notice these aspects of the piece and (B) for you to share your informed, yet original ideas about them. Take a look at these ideas, blend them with your own interpretation and, voila, you've got yourself a solid assignment.