The parents of slain hostage Kayla Mueller say they once asked their daughter to stop doing humanitarian work in Syria but she insisted the struggle of refugees was her struggle too.

Carl and Marsha Mueller say Kayla was the most fulfilled when she was helping to ease suffering in the world, the Arizona Daily Sun reported.

"It was hard not to let Kayla go to all these places she did because it gave her so much joy," Marsha Mueller said. "The more she helped, the more she got."

The Muellers made their remarks Friday night during an event honoring their daughter at her alma mater, Northern Arizona University.

Carl said he remembered asking his daughter to come home.

"I was angry. I said, 'This is not your war, these are not your people. You don't need to die for this. Come home," he said, then read aloud the words she wrote back.

"I do believe this is my struggle," Kayla wrote. "Really, in the end, the real reason that 100,000 lives have been lost in Syria is not because people don't care, or don't have sympathy or compassion. But rather it's because people are under the illusion that this is not their struggle, it is not their people and it's not their concern."

The Prescott couple says since her death, they have had moments of gratitude hearing from people all over the world who Mueller befriended.

"Kayla was like a voice in the deep forest screaming the truth and screaming reality but nobody was there to listen, nobody could hear," Carl said. "But now she's being heard, she's affecting people all over the world."

Mueller, whose death was confirmed in February by U.S. officials, was taken hostage by the Islamic State group in August 2013 after leaving a hospital in Aleppo, Syria.