In 1953, she left the well-appointed corridors of her Hertfordshire school to set up a girls' school in Adamawa province in Nigeria, then a British colony.
According to Joyce Goodman, of Winchester university, Ms Roy was typical of many teachers born in the days of the British Empire. For them, the world was their classroom.
The colonies offered a guaranteed way of advancing their career, while providing British-style enlightenment to heathen children. Many of these women were graduates of Oxford and Cambridge, recruited by the Colonial Intelligence League. The league enlisted only the right sort of girl - those who had attended municipal secondaries or polytechnics need not apply.
The women themselves sought work in imperial outposts for many reasons.
"Some of them definitely had a sense of mission," says Professor Goodman.
"It's not that they necessarily went out to proselytise, but religion gave them a sense of vocation."
This vocation helped teachers to deal with conditions that were far removed from those back home. Ms Roy's role included travelling around mountainous areas on horseback scouting for prospective pupils.
"Some were quite career-minded," says Professor Goodman. "There was a sense of adventure in building something from scratch. These women were teachers, not explorers. But they had real grit and determination. They went out into an unknown world and made it their own. It shows what teachers can do."
In England, it was difficult for successful female teachers to advance into educational administration. The inspectorate was closed to them. It appointed only "washtub women", responsible for inspecting cookery and domestic science. But there were various opportunities in the colonies.
Constance Pike, who had taught at Bedford high school in the 1930s, was given responsibility for education over 15,000 square miles of eastern Africa. Similarly, after moving to Nigeria, Ms Roy was appointed inspector of education in Kaduna province.
Teachers going to a colonial outpost did not need to fear isolation. A British education was an enormous asset in the colonies, so teacher emigres were rarely alone.
Ellen Knox (see box, right), founding head of Havergal college in Toronto, regularly returned to Britain to recruit staff.
In 1913, Ethel Jones left Godolphin school, in Salisbury, for South Africa.
While still at sea, and 1,000 miles from Cape Town, she received a welcoming telegram from South Africa's community of former Godolphin pupils and mistresses. A delegation of Godolphinites met her ship as it docked.
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MOTHER TOOK MY PLACE AT INTERVIEW
Philippa Fawcett may have had a top first from Cambridge, but she still needed her mother's help when applying for a job.
In 1890, Miss Fawcett (right) beat all other candidates taking the Cambridge mathematical tripos. But, because she was a woman, she was deemed ineligible for a BA degree.
In 1901, she accompanied her mother, the suffragette Millicent Fawcett to inspect the Boer War concentration camps in South Africa. She applied to help set up a school system in the Transvaal, and in 1902 she became private secretary to the director of the Transvaal education department. In this role, she developed farm schools for the Boers who lived on the veldt.
She was also appointed lecturer in mathematics at the Normal school in Johannesburg, where she trained maths teachers.
When, in 1905, a position came up as assistant education officer at the London County Council, Miss Fawcett's experience meant that she was the only English woman equal to the task. But she was miles away. So she sent her mother to the interview in her place. She was offered the job and held the post until her retirement in 1934.
VICAR'S DAUGHTER WITH A 'JAGGED EDGE'
Ellen Knox felt God had sent her to Canada. The daughter of the vicar of Exton, previously a government chaplain in India, Miss Knox's first job was at an elementary school in her father's parish.
In 1892, at the age of 34, she retrained to teach secondary and moved to Cheltenham ladies' college. There, a colleague described her as "capable of showing a jagged edge".
In 1894, she was offered a post as founding head of Havergal college in Toronto. She sought the advice of her brother, the bishop of Coventry, who said she had "the makings of an empire builder" and dispatched her to do God's will.
Miss Knox modelled Havergal on Cheltenham, infusing the curriculum with daily hymn-singing and Bible memorisation. Her style was often compared with that of a bishop. She ensured her staff led disciplined lives.
She emphasised the importance of English teachers to the ethos of Havergal and regularly returned to Britain to recruit staff. Once she travelled on the Lusitania, in a state room costing the equivalent of pound;3,000. She died in 1924, leaving an immense estate.