The award was announced on Thursday night in Christchurch.
The 23-year-old will receive $1000 towards her training fees and a set of tools.
It was a "huge surprise" for Miss Kupa to win.
"I'm still wrapping my head around it. I just got off the phone with my dad telling him - it is a huge achievement, really."
Working in construction was "very interesting" and different from what she had done before.
She is working for Breen Construction on the new watersports facility on the shore of Lake Wanaka and praised the company for its "great family approach".
The men were "quite comfortable" with having a female on site.
Other winners were Collision Repair Apprentices of the Year, Cameron Fairless, of Palmerston North and Dylan McGinnity, of Lower Hutt, and Glazing Apprentice of the Year, Daniel Crowe, of New Plymouth.
