"All welcome but will be standing room only, so wear comfy shoes," one of her friends who is helping to organise the service said on Facebook.
Helena McAlpine with her partner Chris Barton. Photo / Natalie Slade
The New Zealand Breast Cancer Foundation paid tribute to McAlpine, described by her daughter Shannon as a "hero mum" in a family notice.
"A champion in the fight against breast cancer, unstoppable in her determination to get a message to every woman in New Zealand about the importance of detecting breast cancer early.
For six years, Helena gave her time and talents to the NZ Breast Cancer Foundation, rising to every occasion with strength, grace and generosity. She inspired us all with her optimism and her commitment to living life to the fullest.
"We at the NZBCF are so grateful for the life of Helena McAlpine and so sad to have lost her - we will miss her so much."
The service will be filmed and uploaded to the internet at about 4pm NZ time so Helena's family and friends overseas can watch the farewell.