@Simpleton no the friend also wasn't wearing a tie in the 1st page, which was still during a class. So it's hard to accept the twist. It feels forced. Maybe I'll just think of the friend as a cross dresser and the big guy is gay.
@DaylightBlue the why: she wants to enjoy living as a student because she never had that experience. The how: the principal of the school is one of her acquaintance that knows her secret, so he can enroll her.