Apparently, the child making the threats is a well known bully with a history of similar behavior. Can she sue the school?
Edit: she is contacting the police and threatening to contact the media. I suggested she retain a lawyer. I'll circle back with updates as this unfolds.
LOUD late night group-protest around the offender's house and throw large fireworks at the front window, torch their car, graffiti their house. Start with that. Seems to work for other people.