However, I still do not think it is a good idea for a teacher to involve a student in the punishment of their peers just as I feel it would be inappropriate for an employer to involve an employee with disciplinary action against their colleagues. For example, if a manager asked me to go to HR to pick up a document with which they were going to write up one of my colleagues, I would be very uncomfortable/reluctant especially if instructed to do so right in front of the colleague in question. This may have been for practicality purposes but it's still just so...icky.
I'm glad things worked out, OP!
However, in office situations it's definitely inappropriate to discipline a subordinate in front of their colleagues. I'm more iffy with students because sometimes it may be beneficial for the students seeing the disciplining.
A closer scenario is one I experienced as an adult:
We used to be super close to DH's cousin (Lulu) and Lulu's DH (Ozzie). We'd go over to each other's houses all the time and we were like a second set of parents to their little ones. We were both poor young couples together so we didn't go out much together. Our eyes were opened to their behavior outside the house, for sure. We decided to catch a movie with Lulu, Ozzie and another of DH's cousins, Sean and his wife, Marie. Ozzie & Sean snuck beer into the theater with them and then thought it'd be great fun rolling the bottles under the chairs on the cement floor during the movie.
They annoyed the other movie-goers and actually started mouthing off to them. My DH and I were sitting in the same row but on the other end and were surprised and annoyed by their behavior. An usher was called in to deal with them and I don't know what was said between them, but when we left the auditorium, the police
were waiting for them in the lobby. I went to join them (why? I hate drama!)
and my DH dragged me away from them, thoroughly ticked off at them and told me that they could clean up their own mess. Now Lulu and Marie were just as annoyed at their behavior but were also treated like criminals because they were with their husbands.
We waited by their vehicle (they were our ride) steaming and when we all piled into their SUV, Ozzie thought it'd be great fun to hang out his window and mouth off to the lady Sheriff from across the parking lot, who then jumped into her car and pulled us over and read him the riot act and let him know she'd be in her rights to make us all get out of the car and show her our ID's and to detain us for 'a long time'. She even threatened to have Lulu, who was driving, take down all our contact information (shades of your DD's dilemma). Which Lulu would have done. So would I. You think it's tough saying 'no' to a teacher? Try saying it to a furious sheriff packing a gun, a baton, handcuffs, pepper spray and a tazor.
Lulu, Marie, DH & I were furious at Ozzie & Sean, not the police officer. I truly believe your DD should be most upset with her friends, not the teacher...if she wants to be upset at anybody. Many people have a 'lie down with dogs, get up with fleas' mentality and your DD will want to keep her eyes open to how their behavior reflects on her. I'm truly glad that they did try to spare your DD punishment, though. Maybe they'll curb their behavior. It's much better to learn these lessons while they're small and the punishments are minor. When one is older, judges and police officers might not be so lenient.