She writes about it over at Oprah.com:
The Reverend Henri J.M. Nouwen, a Catholic priest, analyzes the story of the prodigal son as told by Jesus in the New Testament. Nouwen offers the perspectives of the father and of his sons, the one who returns home after squandering his fortune and the dutiful older son who never left. One sentence hit me like a lightning bolt: “The discipline of gratitude is the explicit effort to acknowledge that all I am and have is given to me as a gift of love, a gift to be celebrated with joy.” I had never thought of gratitude as a habit or discipline before, and I discovered that it was immensely helpful to do so. When I found myself in a difficult situation, I began to make a mental list of all that I was grateful for: being alive and healthy for another day, loving and being loved by family and friends, and experiencing the awesome privilege of working on behalf of my country. By consciously reminding myself of my blessings, I could move from pessimism to optimism, from grief to hopefulness. Nouwen’s book contains universal, timeless lessons for people of all religions, backgrounds and cultures. It really is about how our heavenly Father, God, loves us despite our shortcomings and failings. For me it was a call to the discipline of gratitude and also to forgiveness. And I certainly have had plenty of occasions to use both.
She has more to say on the subjecthere.