If he doesn't do this he will shortly have a courtroom with 50 defendants and a cell phone ringing every minute or so. She was not the only defendant in there that day.
If she didn't know how to turn it off, she should have set it to vibrate only, which would have been acceptable.
She sounds like a teenage drug using idiot. Turning a cell phone off is easy. If she couldn't figure out how to turn it off, how would she ever be able to change the setting to vibrate.