She is now in her 14th year as head of the 540-pupil Wycombe Abbey school, in High Wycombe, Buckinghamshire - a pound;20,000-a-year boarding school for girls. The school motto, appropriately, is "In Fide Vade" (Go Forth in Faith).
Educated at Guildford county grammar school and Manchester university where she read botany and zoology, Mrs Davies said: "I started out in teaching in the 1970s wanting to 'give something back' after my state grammar school education.
"But I felt frustrated by the changes being brought in and sought the freedom of the independent sector."
Her two sons, who are now in their 20s, were schooled privately "because that was the best choice out of the available local schools at the time", she said. This also helped her decision to teach in the private sector.
Mrs Davies said that now, at the age of 53, she would not be returning to the state sector.
"It is too late in my career to change back."
She was the first female deputy head to be appointed at King Edward VI grammar school, in Chelmsford, Essex, which only admits girls in the sixth form.
Mrs Davies was head of Croydon high school, a private selective school for girls, before taking over at Wycombe in 1998.
She joined the GSA in 1990.