Delaware's Supreme Court on Thursday overturned the conviction of a 17-year-old girl in a school bathroom attack that left a 16-year-old classmate dead.

The girl was adjudicated delinquent for criminally negligent homicide by a Family Court judge last year and sentenced to six months in a juvenile facility for the April 2016 death of Amy Joyner-Francis.

An autopsy found that Joyner-Francis, who had a rare, undetected, heart condition, died of sudden cardiac death, aggravated by physical and emotional stress from the fight at Howard High School of Technology in Wilmington. Cellphone video of the attack, which gained national attention, shows Joyner-Francis struggling to fight back and escape as she is repeatedly hit and kicked in the head while her assailant holds on to her hair.

In a unanimous ruling, the Supreme Court agreed with defense attorney John Deckers that no reasonable fact-finder could have found that the girl acted with criminal negligence. Even if she did, the court said, it would be unjust to blame her for Joyner-Francis' death given how unforeseeable it was that the fight would lead to a young teen dying of cardiac arrest.

The Associated Press has not published the name of the girl because she is a juvenile. The Supreme Court in its ruling referred to the defendant using the pseudonym "Tracy," while referring to Joyner-Francis as "Alcee."

The justices said a person can't be held responsible for criminally negligent homicide unless her failure to perceive the risk of death was a "gross deviation from what a reasonable person would have understood." No reasonable fact-finder could conclude that the attack, which inflicted only minor injuries on Joyner-Francis, posed a risk of death so great that her assailant was grossly deviant for not recognizing it, the court concluded.

While the Family Court judge said the girl should have realized that her attack might have deadly consequences because of the close confines of the bathroom, with its tile floor and hard fixtures, the Supreme Court said Joyner Francis' death had nothing to do with those risks, and they were too far removed from the way that she died to blame her assailant for her death.