In October a 21-year-old player in her team, Shelby Turcotte, was diagnosed with lymph node cancer. "That was the final pushing factor for me to do it, it's really hit close to home."
Ms Bradley has pushed her training regime up to gruelling day-long commitments in preparation for the run.
Working as a postie for New Zealand Post over summer, she spent up to five hours biking and then ran for "a few hours" each morning and night.
"I've always been fit and always ran every day so I just upped the training in December - pretty much if I wasn't working or sleeping I was training," she said.
Her experience running the Maine and Boston marathons in previous years also helped, and Ms Bradley will have support crews meeting up with her in each state. She will be linked to GPS through her website run2fightcancer.webstarts.com, so people can track her journey, and will keep in regular Skype contact with her parents Glynis and Steven on the Hibiscus Coast.
The enormity of the challenge had not escaped Ms Bradley, who said she had lost count of the number of people telling her she was "crazy".
"I tend to agree with them actually; if I think about it too much I think 'oh God, I am crazy for doing this'.
"I know this is huge - most people can't even comprehend running one marathon let alone two per day for two months, but to me it's more of a journey. I'm just going to go for it for the experience.
"I want to be an inspiration so people can not just lead a healthy lifestyle but do more to help others, because a lot of the time we get consumed in our own problems, we forget what other people are struggling with."
Cancer Society of New Zealand's national development manager, Philip Hope, said Ms Bradley's effort was "really quite unique" and meant a lot to the charity.
"We thought this was quite an inspirational story and we're really appreciative she's doing this to support us. Its something really positive that people can sit back and be inspired by."
Cancer affects one in three New Zealanders, with about 21,000 people diagnosed and 8000 deaths a year.