"I know when my gran died I was really upset and I didn't want to do anything, but I know she will be watching down on me and doing this would make her feel very proud."
Ms Lee is a representative kayaker and will be competing in nationals this month.
In preparation, she has been running up to 30km a day, kayaking six days a week and going to the gym three times a week.
Despite the intense training, she does not consider herself to be a runner.
"I'm actually not a big runner, I do kayaking and that is my big sport, but I thought that cancer is a big burden on families so I would like to challenge myself."
In the first week, Ms Lee received $300 and hopes to raise as much as she can, saying "every little bit counts".
Ms Lee's grandmother is not the only family member or family friend that she knows of who has been diagnosed with cancer.
"It corrupts families and makes them upset and tears them apart."
For more information and to donate, visit https://give.everydayhero.com/nz/niamh-s-run-for-cancer