"One thing I've been grateful for is the support. Everyone's happy ... it's just love going all around."
A phone call to tell her mum about the result included some screaming.
"It's been a wild day."
She was surprised by her success, Joanna said.
Just before students went into the hall to sit the exam in November, it was postponed by 10 days because of the Kaikoura earthquake. She thought the disruption might have had an impact.
"I remember thinking 'now I can't just forget everything straight away'."
When the exam eventually took place, she did not leave thinking she had aced it, especially as history was "so subjective", Joanna said.
Scholarship exams were hard to prepare for, so she had concentrated on "getting in the mindset of thinking", rather than focusing on learning facts.
Study was not an especially big part of her life - she devoted one to two hours a night. Being in bed before 10pm each night was equally as important.
This year she's studying towards the International Baccalaureate, and thinking about life beyond the school gates.
That will probably involve a joint arts and law degree at a university in Auckland, Wellington, Sydney or Melbourne, if everything goes to plan, Joanna said.
But she wasn't letting her scholarship success go to her head.
"Hopefully I get into uni," the student said.
