Lady Diana was born in Devonshire in England and met her New Zealand husband Neil when they both served in the British Army at the end of World War II.
They married in India and settled in New Zealand in 1950 where Sir Neil and Lady Diana founded their construction business.
The plantings they made on their quarrying operations eventually became the 1100 hectare Peacock Springs Conservation Park.
Lady Isaac was also a huge patron of the arts and her legacy would endure through the Isaac Theatre Royal, the Isaac Centre for Nature Conservation, and the creation of scholarships at Lincoln and Canterbury Universities.
She was awarded a Queen's Service Medal and the New Zealand Order of Merit.
"Lady Diana will be missed immensely but her decades of philanthropy will be enjoyed for generations to come," says Mr Key.