"I went surfing heaps during the exam break and it was good," she said after receiving her crown.
Oxana also picked up outstanding scholarships in biology, chemistry, geography and statistics.
Finding time to study was "tough".
"But it's worth the effort. We only get once chance to do well. You might as well make the most of it."
She's not bad at other activities either, placing second in last year's international geography Olympiad and winning a NZ Geographic young photographer of the year gong.
She even found time to visit the sub-Antarctic islands on an environmental expedition.
Oxana is now studying a bachelor of science at the University of Sydney and made a whistle-stop three-day trip home for the awards ceremony.
After the presentation, she was having lunch with proud mum Natalia and her school principal and dean before hopping on a plane to Australia.
Once she has her qualifications the long-term plan is to gain a doctorate and return home to work in research science, on issues such as climate change, and get into policy management.
"I love Sydney and I love the University of Sydney and I love going surfing, exploring the Blue Mountains. I got back to New Zealand at 2 o'clock in the morning and I knew this was home and I'll definitely be back."
When accepting her award, Oxana took the chance to remind the hundreds of people present about climate change and how everyone can help.
Speaking to NZME, she reiterated "I just want to tell people that climate change is a big issue and we all are contributing to it and all of us must play our part in fixing it."
With all the exuberance of youth, Oxana hopes she and her fellow top scholars will go out into the world and make a difference.
Premier Scholar awards were also handed to:
• Amaan Merchant - Wanganui High School
• Hugo Brown - St Paul's Collegiate
• James Hartshorn - Wellington College
• Martin Luk - King's College
• Soumil Singh - Hamilton Boys' High School
• Tommy Hayes - Auckland Grammar
• Zhengzhe Han - Westlake Boys' High School
• Zhong Qian Huang - Macleans College