She said such brawls were not common but had happened before at the school of 1200 girls.
Flannery was not aware of the video when the Herald called but later confirmed she had begun an immediate investigation.
"This happened in week eight of last term (March 8) and was dealt with through our school processes.
"The video has obviously been uploaded today. We are not sure who has done this but we are trying to find out."
Flannery said disciplinary processes involve meeting families and interviewing students. Any discipline is meted out on a "case-by-case" basis.
"There would be thorough investigations and interviews just to find out exactly what happened."
She was not aware of Auckland Girls' students fighting with students from Otahuhu College in the past.
"Unfortunately things like this happen. We talk to our students about not getting involved."
Often such videos were filmed and posted by non-school students, Flannery said.
The school would work to get the video taken down as soon as possible.
Otahuhu College principal Neil Watson was also unaware of the video but later confirmed one student from his school was involved.
He would not say what punishment if any was handed out.
Watson said media "glamourised" such brawls by reposting the video.
"My concern is that it is glamourised by the media, and you'll post it prominently on your web page to attract more viewers and that perpetuates the problem."
He said fights happened in all schools.
Police Acting Area Commander for Otahuhu Inspector Uraia Vakaruru said no complaint had been made to police about the incident.
However after being notified of the video by the Herald police contacted the schools and confirmed the matter had been dealt with internally.
Police can confirm that this incident has not been reported to police and based on the information available we do not believe any complaint has been laid in relation to this matter.
Vakaruru said police were satisfied the schools had dealt with the matter, and "in the absence of any reports of concern from parents to police no further action would be taken".
The behaviour was very concerning though, Vakaruru said.
"It is dangerous, and reckless and fighting in this manner could cause someone to receive serious injuries.
"The dangers of one-punch incidents resulting in serious injury or even death have been well publicised throughout the country.
"We would also advise anyone who is in a situation where they feel unsafe to call 111 immediately."
The video was posted online this morning and had attracted 13,000 views by lunchtime.
