Lecturer Dr Ann Louise Gilligan told the High Court that the court action by herself and Dr Zappone to have their Canadian marriage recognised here could place her job at St Patrick's College, Drumcondra, at risk.
Dr Gilligan said she had worked at St Patrick's College in Dublin for 30 years. The college was established by the St Laurence O'Toole Trust which has as its manager the Archbishop of Dublin, she said.
Under the Employment Equality Act, if it was deemed the High Court action and her sexual identity were contrary to the ethos of the college, she could lose her job, she said.
As a young woman, she had entered the Loreto sisters but left before taking her final vows, Dr Gilligan said. She met Dr Zappone in 1981. "I remember the first day I saw her. We gradually got to know each other. I fell in love. I was clear about the feeling. I am a lesbian.
"I am quite clear that is my sexual identity. I have no doubts that I was always a lesbian." Before her relationship with Dr Zappone, she had had two brief relationships with men but "that was not for me", she said. "I am a lesbian, of that I have no doubt."
She said she and Dr Zappone had lived together since 1981. At the time of their marriage in Canada in 2003 to see "a sea of accepting faces" ranging from a 12-year-old to Dr Zappone's 80-year-old mother did something enormous in a life where sometimes there had been discrimination against."
She said: "I love and adore Katherine and will be in this relationship all the days of my life."
Dr Gilligan said she and Dr Zappone had made a public commitment to each other at a ceremony before friends in Boston on October 16th, 1982.
This was done after careful reflection and it was a ceremony with a spiritual dimension, she said.