Her coach Chris Pearson said Cox rowed strongly in her recent finals including the North Island Secondary School Rowing Championship at Lake Karapiro last month.
"She is someone who can go a long way in this sport," Pearson said. "She has smooth and powerful strokes."
Cox has only been rowing for three years.
Attention now switches to the final day of racing today where the Western Heights High School under-18 eights will compete in the premier Maadi Cup event.
John Paul College duo Andre Le Lievre and Connor Broughton will also compete in their under-18 lightweight double sculls A final.
The coach of the eights, Glen Reichardt, said the weather would play an important part in the Maadi Cup as the Western Heights crew were lighter than most of their competitors.
A headwind in the race would disadvantage them.
Watch Hannah Cox take gold: