sorry your dd is going through this-but glad the police are acting on it.
just as an aside regarding the ability of private schools to address this issue-it's been my experience as a parent that private schools may talk a great talk on having zero tolerance but when push comes to shove they are not always quick to act in these cases. when i taught at a christian school there were 2 boys (unrelated, diffferent ages) who both had obvious issues with anger management and violence-they had severly injured other kids (preschool and elementary age)-although the school had a zero tolerance policy they always took the 'we need to help these kids' attitude and kept giving them chance after chance after chance. the teachers implored the administration to take action because we feared a child (or teacher) would get permanantly disabled from their behaviours-but not until the kids acted out in a public setting and the police and the family courts became involved did the school admit they were unable to address the problems.
i've had experiences with my kid's current christian school (again zero tolerance policy) wherein i've observed a couple of different boys lose control and have major anger meltdowns (one almost resulting in a teacher being attacked as she tried to wrestle a chair out of the boys hands as he was attempting to bash in another child's head). in both cases i reported my concerns to administration, but until i removed both my children for a week and pointed out to the school and their oversight agency their own policies and how i would hold them civily and crimanaly liable should my children ever be injured due to their failure to enforce their own policies-there was again the "we have to be patient and try to help these kids" attitude.
i would suggest any parent considering a private school do research into the actual usage of their stated "zero tolerance policy"-if a school says they have NEVER had to enforce they are either lying or they are failing to address the situations when they DO occur.
p.s. both boys at my kids school were ultimatly removed and both were mandated by their new schools to attend counseling and anger managment classes (well, one boy's mom refused to aknowledge her son's problems and is now homeschooling him-but since the final straw for her son was when she "went off" on the school board i can see how she did'nt see his behaviour as a problem

).