If you know it wasn't her pursue it! So what if they think you're 'one of those' mothers if you don't look out for her who will. Maybe her regular teacher will agree it would not have been your DD and have a chat with the music teacher. It would do her good to not be so dismissive when communicating(or not) with the kids. Obviously playtime can't be given back to your DD but at least she'll know you and possibly her regular teacher believe it wasn't her. I don't like the sound of the naughty spot anyway