MacMillan is on her second cycle of the life-extending drug Ibrance, which inhibits the spread of the disease.
The drug, and a couple of others Pharmac treats the same, is widely used in other countries for stage four hormone receptor positive cancer. It is seen internationally a game-changer drug, because it extends the median life expectancy by 18 months to two years.
''Greece! Greece has no money as a country, and its government pays for women with stage four breast cancer to have these drugs,'' MacMillan says.
''Pharmac is a 25-year-old system and it doesn't work any more.''
Eventually, the cancer will get her — everyone knows that — but Ibrance would give her another two years with her family. Modern drugs already help her handle the excruciating pain of her illness.
''When you've got fourth stage breast cancer there is no cure, but two extra years with my children and grandchildren, that's a lifetime for women, when the alternative is ... when the ...'' perky voice at the end of the line stumbles for the first time.
Yes, two years to continue to be the loving wife, the mum, the grandmother of one little kiddie, the loyal, respected colleague, and so much more.
''I feel worthless. I feel as if the Government doesn't care whether I live or die. That I don't matter. That my family doesn't matter.''
But talk to MacMillan about the nuts and bolts of the breast cancer that is taking her at a fearsome pace, and with hardly a quaver in her voice she describes the metastatic spread into her cranial vault, neck, shoulder, ribs, hips and pelvis.
That is the voracity of the invader she learned only in May this year had returned to her body.
Now 45, she was first diagnosed with breast cancer in 2011, aged 37.
There is no family history of the disease. There was no warning. One day, out of the blue, she felt a lump.
After a double mastectomy she had 25 sessions of radiation - ''in Auckland, for five weeks on my own,'' then chemo (in Whangārei) and drug treatment, including injecting herself with a hormone suppressor every 28th day for the last seven years.
Seven years in remission, then: ''On May 15th this year I had a scan and found out my breast cancer has moved to my bones.''
The MacMillans have been able to afford two months of Ibrance so far, at $5865 a pop.
As well as both increasing their workloads, they've started a givealittle page to pay for the next script - givealittle.co.nz/cause/donna-needs-your-help
''Insurance pays out when someone has only 12 months to live. Who can say how long I've got? This drug, if I can afford it, could keep me alive longer than that. Or, without it, I might have a few months. Who knows?
''We're looking at remortgaging our house but that idea scares me. When I do go, I want to know that Ewan is cared for, and our kids. I want them to have what we worked so hard to get.
''And there's the bucket list. Mine is wanting to go to Alaska and see the Northern Lights. I've wanted to do that for as long as I can remember. The other thing on my list is to take the whole family, all of us, on a cruise.''
And there is the anger, the frustration, that victims of an accident of health don't get the support victims of accidents do.
To fund one woman's optimum two years of life once she requires a drug like Ibrance, or another called Kadcyla, would cost the government - or Pharmac, the handler of the public money - around $140,000.
That would be similar to treating many illnesses over the same period, MacMillan says. And, not that she wishes to discriminate or point fingers but she points out that, theoretically, a prisoner who seriously injured himself trying to jump the fence would get the public health care he needed, and it already costs the country $99,000 to have him locked up.
Not a fair example? Well, when you can only afford one more month of an exceedingly expensive drug treatment, and once it stops death will be hastened by the rapidly spreading cancer, not a lot seems fair.
Donna MacMillan's plea to Pharmac — ''Please pay for my drug so I can have more time with my family'' — is the same being made by hundreds of New Zealand women and their loved ones.
MacMillan is a strong supporter of the petition that women with breast cancer, their family, whānau and supporters are taking to Parliament on 16 October, calling for the funding of the breakthrough medicines, Ibrance and Kadcyla. The Ibrance petition has around 30,000 signatures; the Kadcyla petition more than 1500.
This year, about 300 Kiwi women and handful of men will be told they have incurable advanced breast cancer (ABC), also called secondary, stage four, or metastatic breast cancer.
Because of the nature of the fast moving, advanced cancer, those 300 will become part of the constantly changing population with the disease. Each year, as many join the ranks, a similar number dies.
Pfizer New Zealand has introduced a Patient Assistance Programme to reduce the cost of Ibrance for eligible patients, while Pharmac considers the company's application for funding. Pfizer NZ applied for Ibrance to be funded in February this year, and Pharmac has not yet made a decision.
New Zealand patients who meet the eligibility criteria and have already purchased eight packs of Ibrance from a pharmacy, can get the next four packs free.
Anyone currently taking the drug is encouraged to talk with their oncologist to find out more about eligibility, the Breast Cancer Foundation NZ urges.
Meanwhile, a recently released Breast Cancer Foundation report states the struggle of stage four patients takes place out of the spotlight that celebrates the "success stories" of early breast cancer survival.
''We learned that New Zealanders with ABC die faster than people in other countries, that many of them get less treatment, and that the health system disadvantages them in many ways. This needs to change, right now,'' says the report called I'm still here.
Many with advanced stage four will end up feeling unseen, forgotten, isolated. They'll feel that the health system has turned its back on them — just as Donna MacMillan said.
''I feel that I don't matter.''
The report's title, I'm still here, came from a conversation with Tamara Malone, a mother-of-five diagnosed with ABC in her late 30s.
''She told [the foundation] how vastly different her experience as an ABC patient was from her first diagnosis of breast cancer; how she felt the health system had given up on her, long before she'd given up on herself.
"She died in January 2018, aged 41.''