A police spokeswoman said officers were notified on Monday of the incident.
The victim's mother said the incident stemmed from a Facebook fight between her daughter's friends, and another teenage girl from a nearby town.
The teens arranged to meet at 2.30pm outside the school, but when one of the groups showed up, they were allegedly met by a teenage girl and a group of her adult relatives, including a woman said to be a 20-year-old mother.
The victim's mother said there was a fight between one of her daughter's friends and the other teen.
Afterwards, she said the 20-year-old attacked her daughter, and that was the incident caught on film.
The college the fight happened outside is yet to respond to Herald requests for comment.