Well, a possible theme could be discovery. The girl could have discovered something about herself, like a new talent or a hidden emotion while in the bathroom. Fear could also be a theme if there was something scary or unexpected that happened in that private space. And of course, there might be a theme of secrecy, if there was something she was hiding or something hidden in the bathroom that she found.
Privacy is a likely theme. The bathroom is a private area, and the girl's story might revolve around the importance of having that private space or something that violated her privacy. Also, growth or change could be a theme. Maybe she had an epiphany while in the bathroom that led to her personal development.
One possible theme could be isolation. Bathrooms are often private spaces, so the girl might be experiencing a sense of being alone or cut off from the outside world. Another theme could be self - reflection, as it's a place where people often think about themselves.