As a current teacher/former school library media specialist, this burns me, first, because of copyright issues. I know, I know, "everyone does it", but these movies have NOT been bought through an educational service for big $$ so they can be shown legally to kids, they've been brought from home, I'm sure. Second, every school district has in place media viewing guidelines, that every staff member should know and follow. (Usually requiring use of a parent permission slip for certain ratings, and at least a suggestion that the movie should "fit the curriculum".)
As a parent, I would do as others have suggested, drop the teacher an email stating that you've chosen not to have your daughter watch this film, and that you'd appreciate her consider using a permission form in the future. If you wanted to, you could ask the administration (discretely, without using the staff member's name) if there is a viewing policy in place and, if so, if you can have a copy of it. Asking for it alone may be enough to "nudge" them into reminding the staff as a whole to follow it.
Terri
(Who is NOT showing any movies this last ten days of school!)