Bad experience from service provider

There are high school learner that opened a WhatsApp channel named it after the school. My daughter has been humiliated on the channel called the most embarrassing words, I want to find out who are the culprits because the screenshots are circulating everywhere. She's falling into depressed and isn’t even comfortable in attend school anymore,,I went to the police station to open a case and i was told there's nothing they can do about the situation.