The couple's work continued after they arrived in Whanganui in the mid 1980s, and she initiated a Whanganui branch of the United Nations Association of New Zealand (UNANZ).
Their peaceful garden and house, known as Rumah Brooke, was the scene of many gatherings.
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In 2000, their Operation Peace through Unity initiated the Handspan peace sculpture set in Pukenamu/Queen's Park.
Gita was born in Copenhagen on July 29, 1931. Her father was a Lutheran minister and she was the younger of two sisters. She spent her first five years in Tamil Nadu, India, where her parents set up a church and her sister died.
The family returned to Denmark as World War II began, and the country was occupied. Gita's father helped smuggle Jews out of Denmark and into neutral Sweden. Her uncle was arrested by the occupying Germans and interviewed and tortured by a Danish collaborator.
Despite her school years being interrupted by the war, Gita was "superbly educated by the university of life", her friend and Operation Peace through Unity trustee Basil Avery said.
Perhaps it was the events of the war that made Gita uneasy in the world, and began her lifelong work for peace.
As a young woman she gave birth to a daughter, Anna, and took on secretarial work at Copenhagen Hospital. It was a struggle to provide for her daughter.
In 1963 she married Swedish manufacturer Douglas Keiller, who adopted Anna. Gita was very fond of his mother and they lived in Govik, Sweden, for 15 years.
She met Anthony Brooke, who was nearly 20 years older than her, when he needed a place to stay and her husband invited him to Govik. The two shared an interest in spirituality, philosophy, astrology and had many talks.
In 1975 they co-founded Operation Peace through Unity, a "high level forum", Avery said. It's recognised by the United Nations, despite having no formal structure and having "co-workers" rather than members.
"The aim is to find points of commonality, so that people don't disagree, and move on from there. It's the glue that binds all sorts of disparate groups together," Avery said.
After Keiller's mother died, Gita took up a travelling life with Anthony. From 1976 to 1988 they lived on travellers' visas, often visiting strife-torn countries others were trying to leave.
They went to conferences and launched campaigns across the world - disarmament, indigenous rights, peace. In 1981 they married, and spent two years in the United States in Santa Fe, New Mexico. That's where they started the Operation Peace through Unity newsletter, Many to Many.
The two made a formidable team, friend Kate Smith said.
"Gita would stand back and listen and watch, while Anthony was exuberant and ebullient."
Anthony was a seasoned traveller, but Gita wanted a home. Through a chance meeting they settled on New Zealand and came to Whanganui. The house they bought in Allison St matched one Gita had seen in a dream, and was similar to Anthony's former home in Sarawak.
In Whanganui they carried on their work, with Gita tending their peaceful garden, talking to the plants and feeding birds and stray cats.
In 1989 they set up the Operation Peace through Unity trust, and Gita organised peace ceremonies at the Handspan sculpture.
Anthony died in March 2011 and Gita carried on, composing her last meticulous Many to Many newsletter in November last year. It's now distributed to 55 countries.
Operation Peace through Unity carries on as a charitable trust, with Roger Morrison and Basil Avery as trustees, advised by a board that Kate Smith is a member of.
Gita would not be dismayed by the present state of the world, Avery said. She had predicted a period of painful turmoil before a new and better order.
"Old institutions, structures and motivations are crumbling. The new is beginning to emerge," he said.
The advisory group is settling Gita and Anthony's affairs, and may keep Rumah Brooke for use as a retreat.