One of her patients, a New York City real estate broker, lost her only child in 2002. Then a 26-year-old MBA student in France, Jeremy was killed in a car accident.
Iris, who did not want her name used, said the therapy was "phenomenal" and helped save her life.
"You never get over it, but you can be with yourself again," she said.
At first after Jeremy's death, Iris was in shock. "It's the shock that helps you," she said. But then, as it wore off, "I was in such horrible pain aching for him."
Now, after 16 weeks of reliving the death and recording her feelings, Iris said the memory of her son "is always with me, but the realization that he is not on this earth is apparent now."
"I look at things differently now," she said. "I am able to feel blessed that he was in my life and I was his mother. I couldn't feel that before."
But now, as Petrillo's own 13-year-old son and two sisters mourn her death, they too, face a great loss, according to Peter Goodrich, a family friend and lawyer. "They love their sister."
"They don't need any more publicity," he told ABCNews.com on Wednesday, the day of her wake. "It's hurtful every time."