That is not what "boxed" means in English when referring to people. A "boxed girl" would be a girl who has been hit (a frequent form of corpal punishment in the premodern world was to "box" (strike) the punished individual's ears, usually lightly, not that the abusive would stop there).
I'm guessing what was intended was "a girl in a box" (as in the figurative sense of a person being trapped in a predicament).
A better phrasing would be "boxed-in girl."