"For me the point was that I've not felt free to be openly gay in a public way," she told CBC's The Morning Edition host Craig Norris in an interview Thursday.
"I haven't been open with students that I've even been working with that were LGBTQ [lesbian, gay, bisexual, transgender and queer]," she said on the day before a historic U.S. Supreme Court ruling gave gay people the right to marry across the country.
"I haven't been able to be open with parents, and that brings you to a place of shame," she said. "For me, shame is not of God, it makes you feel like you're a mistake or a bad person. It's not a good feeling, it's quite suffocating for the soul."
'That haunted me'
Grundy documented her story in a new book called, A Deepening Life. In part, it describes what she calls "coming out to herself" at age 33, while working in the Catholic school board. Gradually, she began to tell other people about her sexual orientation.
"A number of my colleagues did know, my close colleagues," she said of her orientation, but she felt the need to keep it a secret because of the teachings of the Catholic church. "I think it's safe to say there's a lot of fear, a lot of vulnerability," said Grundy, who was in a relationship for over a decade and worried about losing her job because of it.
For Grundy though, it wasn't just the effect her secrecy had on her own life that concerned her. It was what she was modelling to kids who were gay and lesbian.
"Because here I was encouraging and challenging them to be true to themselves and to celebrate their God-given potential and their goodness, and I wasn't doing that," said Grundy.
"I can't tell you how much that haunted me."
She said that she did ask a few former students about it, and they said they recognized the position she was in, teaching in a Catholic school, and they understood why she couldn't be open.
Walking a tightrope
Grundy was careful to say there wasn't any official policy preventing Catholic school board teachers from being gay, but rather the teachings of the Catholic church, which says that same-sex relationships are "intrinsically disordered."
That's slowly changing. In October last year, Catholic bishops recognized the positive aspects of gay relationships, but said gay unions couldn't be considered on the same level as those between a man and a woman.
And in 2012, Ontario passed legislation that ruled Catholic schools must accommodate gay-straight alliances, to support gay kids in the Catholic school system.
"I talk in my book about walking a tightrope, and I think many senior administrators in Catholic boards walk those same tightropes, because, again, we're contracted and we need to abide by the official teachings of the church, and it's not always easy," said Grundy.
Grundy said she sees attitudes towards homosexuality changing among young people, and she thinks that's the key to getting openly gay teachers in the Catholic school board and in the public school board.
She recounts a time that Rosie Cossar, a rhythmic gymnast who has competed in the Olympics and is also openly gay, and the students asked questions about being in the Olympics first, not her sexual orientation.
"That brings us a long ways from when I was in family life classrooms 25 years ago, and put the word 'homosexuality' on the board and literally saw the body language of people cringing in their seats," said Grundy.
In her retirement, Grundy will be writing the curriculum for a teacher training course, giving talks and retreats and paddling her kayak.