I cannot see myself making a statement to the entire class about what they wear and I am never alone with a student, ever.I would make a general statement to the class about appropriate attire without pointing fingers at the intended target. Maybe that would be enough for her to get the hint.
In addition, I would make sure that I was never alone with this girl, or any girl for that matter in order to avoid any he said/she said situations.
PS As a C/O in a jail, I sometimes have to deal with female inmates and this is exactly how I handle them. Female inmates love trying to jam C/Os up. They will frequently flash us as we make our rounds, walk around naked in their cell when they know we're walking around or even flash us their clams while they're out at yard in the summer.
