The 18-year-old says her parents were "awesome" and "100 per cent behind me" but some of the staff at Rangitoto College were less enamoured with the decision.
"Some of my teachers weren't too happy but I hope now it is okay," says Dennison. "I was missing a lot of classes anyway through hockey."
The extra focus was rewarded as she was selected for the tour to the US in August, then the subsequent Oceania series against Australia, and has now racked up six matches.
It was still a nervous wait on Champions Trophy selection in December.
She thought she had missed out when she heard the team had been announced and she hadn't received a phone call.
"There were a few tears," says Dennison, "but it turned out I had a flat cellphone battery. I was probably crying more when I realised I had made the team."
For Dennison the ligthtbulb moment when she realised that the silver fern could be a possibility came in 2009.
"I decided to do everything I could," remembers Dennison. "I was down at the turf practising all the time. I had a lot of friends in rep teams and we would train on specific things and I was always bugging coaches to do extra sessions."
She made national age group teams in 2010 before her call-up to full national honours last year. The Black Sticks were granted some time off over the Christmas break but Dennison, like the rest of the team, had to stick to strictly agreed training schedules.
She went running on Christmas Day - though it was definitely 'pre-turkey' - and another long jog on New Year's Day, sandwiched around other aerobic work.
Dennison knows little about Argentina; only that it will be hot, with temperatures higher than 30 degrees Celsius after nightfall possible, and that the team's favourite game in the hour-long journey from their central city hotel to stadium on previous tours was counting the stray dogs.
Dennison, who was always a striker for her club and province, has mainly been used at the defensive end for the Black Sticks.
"I remember the first few trainings and I was put in the halves," says Dennison. "I thought it could be an interesting experience but later on I thought; 'wait a minute - is this permanent?"'
And yes, before you ask, Dennison is named after the classic Fleetwood Mac tune, a big hit on their breakthrough self-titled album of 1975.
"My parents really like the song," laughs Dennison, "especially my Dad. I don't mind; I think I first heard it when I was eight and it's on my Ipod now. But none of my friends tease me about it - no one in my age group knows who Fleetwood Mac is."
The Black Sticks face South Korea, Great Britain and Argentina in the four nations tournament which begins on January 18. From there, they travel to Rosario to play practice matches against Japan and China ahead of the Champions Trophy which starts on January 28 (January 29 NZT).They have not yet left the country but the women's Black Sticks have already suffered a setback.
Assistant coach Greg Nicol crashed off his bike last Friday afternoon and will now not be travelling with the team departing for Argentina today.
Nicol suffered a deep gash to his leg after falling from his bike when attempting to jump a kerb on his ride home from work. Hager drove him to North Shore hospital, where staff initially though a skin graft would be necessary before eventually settling for 15 stitches.
"It's far from ideal but we have to live with it - s**t happens," says Hager. "It just means my workload increases for the first section of the trip."
Hager, already known for the massive days he puts in where he often rises at 5am, will be running solo at the four nations tournament, as his other (part-time) assistant Chris Leslie is tied up with family commitments until January 23.
Nicol and Leslie are expected to arrive in Argentina just before the start of the Champions Trophy on January 28.
