The worst they could do is sue the police department. No DA would even bother giving them the time of day for attempting to press charges on a girl who had a freakout after watching their criminal kid take her best friend hostage with a knife. A far more logical explanation would be that Sal squealed and pinned the blame on the guys she helped rob the other convenience store. Which would make for an actual dramatic plot, the guys she ratted out are getting out of prison.
The real issue is that anything her parents do to keep her out of prison fly against the narrative that her parents are terrible people who dislike their daughter. If that were true then they wouldn't have presumably spent tens of thousands of dollars sending her to boarding school when juvie was right there.