Without Ibrance, the cancer will spread extremely rapidly, and she might be looking at only months. Her insurance company will not pay out early on her life cover, which it normally would if she had less than a year to live. In a Catch-22 situation, having the pay-out earlier would mean the MacMillans could afford the treatment which might then extend her life more than that predicted year.
Read the small print, consider the implications, she now advises everyone.
''I'm doing all right,'' a tired MacMillan said on Boxing Day from her mother's home in Stratford, Taranaki.
''We're scraping together the money for month number six but we've come to the decision we might not be able to afford another round after that. We know stopping the Ibrance will greatly reduce my life span, but we can't keep up the struggle.''
This year she knocked off a bucket list item, seeing the Moeraki Boulders on north Otago's coast.
''People have said 'why would you go all that just way to see rocks' but it was absolutely amazing! I've wanted to see them since I was a little girl.''
Next to knock off, should the family ever get the money together, is a family cruise.
MacMillan knows the cancer will win, and other drugs enable her to deal with the pain, but the extra time Ibrance could give her with her husband, children and grandchildren - "that's a lifetime''.
Meanwhile, they both work two jobs - at least, she does when she's well enough - to pay the monthly medication bill.
It has been a hard year, in which the cancer returned after being in remission for seven years - a terribly aggressive onslaught on her body, several surgical procedures and living with extreme fatigue and pain.
Among kindnesses shown to them during the year was the company her husband and daughter work for sponsoring one month's treatment.
''That was so wonderful, we are so very grateful.''
A Givealittle page has also helped raise nearly enough for a month's course of drugs. (givealittle.co.nz/cause/donna-needs-your-help)
Pharmac's recent decision does extend to funding patients after 11 months on the main two drugs.
''But that's too late for those on it now. We don't meet Pharmac's criteria of 'first line of defence'. In fact, no one does because the drug is for people far beyond that stage.''
MacMillan is not alone in her struggle to afford the cancer cell division-inhibiting drug or her expectation that Pharmac should be footing the bill.
More than 30,000 people supported a Breast Cancer Aotearoa petition delivered to Parliament in October, calling for at least two life-extending drugs to be funded for nearly 300 New Zealand women and a few men with late stage, metastatic breast cancer.
Funding her optimum two years of life with Ibrance would have cost Pharmac about $140,000, MacMillan said.
It would give her more time with her loved ones and, in the end, take away the burden of making a life and death decision based on a family's inability to meet a drug's cost.
