"I'm very, very close to my nana - all her grandchildren are," she said. "We spend a lot of time as a family together."
Her grandmother's first diagnosis with breast cancer five years ago hit the family hard, and the second cancer, discovered two years ago, was an even bigger shock.
"Nana is the rock of our family, so her getting sick was a really big deal for us all."
Her grandmother was successfully treated and was now in good health - but Flynn was aware that many women were not so lucky.
"I came on board with the NZ Breast Cancer Foundation because of the work they're doing to educate women about the need to be proactive about breast health, and the support and information they offer women who've been diagnosed."
Evangelia Henderson, chief executive at the New Zealand Breast Cancer Foundation, said she was thrilled to have Flynn on board as ambassador.
"Gemma is so inspiring to young women, and is known for her hard work and commitment in her sport. I believe that when she tells women to look out for their breast health, they'll listen."
The message of early detection was vital because the earlier a breast cancer was found, the greater the chance it could be successfully treated.
When a cancer was found on a mammogram, a woman had a 92 per cent chance of being alive 10 years later. With a cancer found as a lump or other symptom, 10-year survival drops to 75 per cent.
Mammograms were recommended for women over 40 and were free from age 45 to 69.
The foundation said women of all ages should know the normal look and feel of their breasts, and report any changes to their doctor.
One of Gemma Flynn's first acts as an ambassador for the NZBCF will be to walk the 21km Pink Star Walk in Christchurch on October 29, along with fellow ambassador and ex-Silver Fern Maree Bowden.