She was teaching inquiry learning when she ''died'' in front of her year 8 Napier Intermediate pupils.
The mother-of-three had suffered a cardiac arrest. Without warning, the 45-year-old's heart had stopped beating.
But as she lay face down on the classroom floor, something amazing was about to happen involving brave pupils, quick-acting teachers, the kindness of strangers and a deputy principal taking on the school field in high heels.
Mareikura is sharing her story to raise awareness around CPR and automatic external defibrillators (AEDs).
"I wasn't sick, I didn't feel anything coming on ... if it had to happen to me, it happened at the right place, at the right time, with the right people around me," Mareikura said.
Former teaching colleague Kelly Durston, now an Eastern Institute of Technology tutor, was alerted when one of Mareikura's pupils ran into his class in November and said she had fallen.
"I assumed she'd twisted her leg, but she was face down on the floor and looking a bit purple ... she wasn't breathing."
Days earlier the army territorial completed a combat lifesaving course. The school had also held a first aid refresher course a month before.
It was surreal switching from sitting on the floor teaching algebra to performing CPR on a colleague.
"I was just doing what I knew I had to do. It was almost like I wasn't thinking."
Deputy principal Lou Taylor was unloading trophies for the final assembly when a colleague rushed up.
"She said 'It's Benita, defibrillator, go'."
The closest defibrillator was 550m away at Jetts Fitness so she switched on the hazard lights in her Toyota Auris and put her foot down as trophies rolled and clanked behind.
"I was saying to myself 'Do no more harm', so while I was kind of speeding I was really aware I needed to be sensible, too."
With the engine still running, Taylor pulled the gym door open and spotted the attendant eating lunch.
"I just went 'Oi, defibrillator, now'. He came running out and I just grabbed it."
Taylor remembers the moment an ambulance officer — emergency services arrived just after the defibrillator was used — saying Mareikura was breathing on her own.
"It was like 'Oh my God, we've done good'. It was an absolutely amazing team effort."
For Durston, the moment was overwhelming.
"I was shaking when all the adrenaline wore off ... [now] I feel very proud."
He later bumped into Mareikura's husband, Lee, in the supermarket.
"He gave me a big hug and said 'that's the best Christmas present anyone could ever give'. That was pretty emotional in the middle of the supermarket."
Mareikura, who has taught at Napier Intermediate for 24 years, spent two weeks in Wellington Hospital and returned to the classroom this year.
Cardiologists said the cardiac arrest was caused by a rare "electrical fault". A defibrillator is now implanted in her body.
Heart Saver NZ managing director and medic Mike Mander said the earlier CPR began and an AED was used the better the chance of survival for the 2000 people who suffered cardiac arrest each year, of which about 1500 died.
Survival rates fell from 90 per cent if an AED, which cost less than $2000, was used within one minute to 50 per cent after five minutes and 20 per cent after eight minutes.
"Benita's experience just highlights how important it is to be ready for a medical emergency in any situation."
Heart Saver gives away two AEDs to entering schools, sports clubs, community and not-for-profit groups every month through the Become a Heart Saver campaign on www.heartsaver.co.nz
Mareikura said her school had been motivated to buy its own AED following her "death".
Because that's what it was.
"I just collapsed and died in front of my class, until they were able to bring me back. What do you say to somebody [who does that], except thanks.
"Thank you, I really, really appreciate it. Love, hugs, kisses. You can't say much else."