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— -- More than a month after her daughter was killed in Iraq, Lori Witmer received a very special — and unusual — tribute to her daughter.

A former Army Ranger from Florida completed a grueling, non-stop 175-mile run from Miami Beach to Key West to honor her 20-year-old daughter Michelle, who was killed in an ambush in Baghdad last month.

Michelle was serving in Iraq alongside her sisters Rachel and Charity on April 9 when she was killed in an insurgent attack. The two surviving sisters decided against returning to combat in Iraq after Michelle was killed, but are supporting the Defense Department's homeland security missions in Wisconsin.

When Alex Estrella, a former Ranger who served in the first Gulf War, called up the Witmer's home in New Berlin, Wis. and told them about his plan to honor Michelle's memory, Lori was immensely touched by the gesture.

In her first interview since her daughters decided against returning to Iraq, Lori told ABCNEWS' Good Morning America the gesture prompted her to buy a plane ticket from Wisconsin to Florida to support Estrella despite her grief.

Mixed Message: Be Sexy But Still Pure

It was a punishing run done non-stop over four days with a support teams of U.S. Army reservists running behind Estrella to provide him food and water. For the last few miles of the run, the former Army reservist crawled for a while and was then pushed across the finish line in a wheelchair.

But for the former military man who served with the 1st Brigade of the 101st Airborne Estrella during Operation Desert Storm, it was well worth the effort.

"I was doing this for a very special woman, a woman that lost her life in an ambush," he told Good Morning America. "When I was in [Operation] Desert Storm… we were in and out really quick. And this time, compared to the situation, there's casualty list growing every day. This young woman had a full life ahead of her."

Michelle was posthumously awarded a Bronze Star medal and a Purple Heart for her service.

Mixed Message: Be Sexy But Still Pure

More than five weeks since her daughter was killed in Iraq, Lori says she still suffers the physical ramifications of grief. "Some days, some minutes, I'm fine. Some hours I can talk and I can laugh. Others, I can't even hold my head up," she said sadly, before adding, "She was a hero. She is a hero."

It's a view Estrella shares. "I was doing this for a very special woman, a woman who lost her life in an ambush," he said.

During her time in Iraq, Michelle took time off from working as a military policewoman to help the orphans at the Missionaries of Charity in Baghdad.

Donations and contributions from Estrella's race will go toward a number of charities and caused supported by Michelle during her extraordinary life.

For Lori, it's heartwarming to see her daughter's memory being kept alive. While the Wisconsin mother did not take a stand in Rachel and Charity's decision not to return to Iraq, she's grateful to have her other two girls are at home with her.

"I'm so comforted to know they are here," she said. "I can't imagine going through another year and another five weeks like I have just gone through."

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