You are making a lot of assumptions. The father has never said she's been involved in multiple fights with this group at school if anything the opposite. His beef with the superintendent is that they suspended the bullies but he thinks if they were arrested somehow the student bystanders wouldn't have shared the videos.

There's absolutely no way to ban cellphone use in schools short of having a prison like inspection system

Everyone is or has been bullied. There's absolutely not enough money in the school system to manage what is thousands of teen students personal interactions both in person or online every single day including weekends. A typical prison is 4 to 1 staff. A highschool it's not uncommon to have 30-50 students per staff member. It's just literally impossible to handle. If the bully has developmental/aggression issues and is on a non-standard education (e.g IEP, 504, etc) they cannot be legally expelled. Other than that yes the students can be expelled and if your made-up theory that the same bully regularly assaulted her then they'd have been expelled. Even then she'd have just been bullied online which was actually the father's complaints. It wasn't the fight it was what was going on on social media. Truth is that if your child has a persistent bully, don't rely on the school it's not a daycare, or prison, and it's not a justice system. Seek retribution from law enforcement and a judge, you don't need an attorney to do this.