"It gives her that: Mum and Dad were married and that she has something more precious to hang on to."
David popped the question on Tuesday, following Rachel's first session of chemotherapy at Auckland Hospital's oncology department.
He was planning to take her to the Robert Harris cafe in New Lynn, where they had first met in person, but Rachel was confused so they went instead to the Auckland Domain, near the hospital.
David said he was nervous as he proposed: "I said her name in full and would she be my wife."
Rachel picks up the story: "I said, 'I knew you were going to ask me'. I said yes, of course."
The couple, together for more than three years, now have to organise a small wedding for family and friends around cancer treatment.
David, a steel gate maker, and Rachel, whose illness has forced her to stop her work as a graphic designer, are speaking out about her illness to raise awareness of melanoma and to encourage people to protect themselves from excess sun exposure.
However, in Rachel's case it is not clear where the cancer began. She recalled a couple of episodes of sunburn, but said she was not a sunbather and no evidence had been found of a primary melanoma tumour.
Melanoma is mainly known as the deadliest form of skin cancer and is linked to blistering sunburn years earlier, but primary melanoma tumours can also occur in places that don't see the sun, such as the oesophagus. And it is reasonably common for people to be diagnosed, such as Rachel, with melanoma in organs in the absence of a primary tumour.
Auckland Hospital oncologist Dr Mike McCrystal said this occurred in up to possibly 30 per cent of cases where the cancer had spread to organs before diagnosis.
Rachel had an operation to remove a 35mm brain tumour and keyhole surgery to remove a small tumour on her lung, but cancer cells have returned in both places.
She had radiation therapy, which caused her hair to fall out and has now begun chemotherapy. If the tumours don't respond to the chemo or her body reacts badly, she may be eligible for treatment with ipilimumab, an expensive drug not yet funded by the public health system, but made available free for some patients on compassionate grounds by its manufacturer, Bristol-Myers Squibb.
Dr McCrystal said 24 patients around New Zealand were receiving the drug on that programme, but the company was closing it to new patients in mid-April.
Rachel said she had lived an active, busy life, and was trying to cope by "getting on with things every day as I can".
But the hardest thing emotionally was: "Saying goodnight to Mia."
Melanoma
* New Zealand has one of the world's highest incidence and death rates
* More than 2000 new cases diagnosed and about 300 deaths a year