In four months' time, the 16-year-old, originally from Queenstown but now living in Timaru, will make a sacrifice many teenage girls couldn't fathom - she will shave off her long, blonde tresses in front of thousands of people at the Timaru Relay for Life event.
''I'm going bald. I'm pushing it to grow more now - I know I'm shaving it for a good cause, so the longer it is, the better.''
On Saturday afternoon, Hannah and her father, John (57), were at the finish line of the 2014 Silver Fern Rally armed with collection buckets, aiming to help Hannah reach her fundraising goal of $10,000 for the Cancer Society.
For Hannah, the loss of her locks is also about showing support for her dad, a Queenstown businessman who has endured three bouts of cancer.
Mr MacDonald was first diagnosed with melanoma when he was 30 and was diagnosed with a second melanoma in 2012.
Six months later, he was diagnosed with urethral cancer.
''Although we've got a long way to go, we've had a clear test.
''It's been a long 18 months not knowing.
''Hannah didn't particularly want to talk about it before, but this is her way of dealing with it.''
Hannah said her father was her ''main motivation''.
''The fact that I felt like I couldn't do anything, I got this idea ... so many people I know are affected by cancer; everyone's got a story.''
Mr MacDonald said he was ''incredibly proud'' of Hannah's decision, which he described as a ''huge call''.
The teenager's fundraising mission was supported by the Silver Fern Rally, which adopted her as its official charity - supporting Mr MacDonald and two rally drivers who died from cancer in the past two years.
Stages in this year's event were named after Willie Rutherford and 2010 winner Andrew Grundy.
On Saturday, Vince Bristow and Dean Mitchell, of the United Kingdom, created history in Queenstown as the first international team to win the rally, in a Bryce Biggs-supplied Ford Escort. Mr Bristow said he was ''chuffed to bits'' to win.
''It's a great event, fantastic people and a lovely country. This is the fourth time I have done the event and it is good to finally get to the end at the front.''
Mr MacDonald sold his business, Quickstop Auto, to focus on his recovery but hoped to finally enter the rally in 2016.
The 1979 National Novice Champion and Queenstown Car Club member bought a Mazda RX7 when he turned 50, with a view to racing it in the rally - something he has entered several times, but never actually competed in.
''I still haven't done that ... they're two years apart, so maybe the next one.
''The pressure is on me now.''
Donations can be made to Hannah's Shave for Cancer at fundraiseonline.co.nz/HannahsShaveforCancer
