Rotorua Marathon race ambassador Rachel Grunwell running for a powerful purpose

(From left) Arina Larionova, Rachel Grunwell, Tess Garner and Christina Fordyce in Brady's Bunch attire. Photo / Supplied

As race ambassador for the Rotorua Marathon, few people know the unique and magical appeal of New Zealand's most iconic marathon better than Rachel Grunwell.

Yet on Saturday, Grunwell will take to the streets of Rotorua fuelled by a different set of emotions as she tackles the 10km event in memory of Brady, teenage daughter to one her best friends, Christina Fordyce, who lost her battle with cancer in March.

Diagnosed with cancer just before New Year's Eve, Brady, a student at Mt Roskill Grammar School, died in mid-March at the age of 16.

"I've known Brady since the day she was born," said Grunwell.

"She was beautiful, kind, and had the biggest smile. There is a pain that comes from losing someone to cancer that cuts so deep it's indescribable.

"My heart shattered into a million pieces over her death - and also the heartbreak watching Christina lose her daughter who brought so much sunshine into her life."

Ronald McDonald House helped Christina stay by Brady's side through the 11 weeks in paediatric intensive care and so Grunwell, along with a group of six including Christina and her son Ben, are running courses with T-shirts emblazoned with Brady's Bunch to fundraise.

So far the group has raised more than $5000 for Ronald McDonald House and Grunwell hoped the day would be a celebration of Brady's glorious life.

"On the day, it would be too easy to cry our way through this event," said Rachel, who was born and raised in Rotorua.

"Brady was supposed to run this day but we want to try and smile instead and remember Brady and how much fun she would have had.

"This day is about celebrating a brave little girl who was so loved and is so missed. It's also about giving back to a great place."

On race day, Grunwell will be guiding visually impaired athlete Tamati Pearse in her capacity as an ambassador for Achilles.

Achilles is a charity that helps Kiwis with disabilities to participate in mainstream running events.

Co-guiding alongside Jonathan Hagger, head of Rotorua Hospice, the event will take on a special meaning for Grunwell, in a race she describes as her "favourite in the world".

"This year will see my tears mix with rain if the weather forecast is correct and it's raining that day", she said.

"I'd do anything to repair the hole in my friend's heart in losing Brady. But the race day will also bring smiles.

"This run will see Brady's Bunch raise our feet for a run goal. But also raise cash for Ronald McDonald House. The run will be for a powerful purpose."