TRENTON, N.J. ? Michelle Gwin spends most of her time caring for her severely ill 3-year-old daughter, an around-the-clock job that helps keep her mind off something just as worrying: her husband’s military service in Iraq.

“We have bad days, but we try not to have those too often,” she said by telephone from Durham, N.C., where her daughter, Ashleigh, is being treated for Krabbe disease.

“I believe that God put us on this earth, and he has a time to take us off,” she said.

In Iraq, 1st Lt. Howard Gwin said he often listens to Martina McBride’s “In My Daughter’s Eyes” to remember Ashleigh, his “princess,” and the couple’s other daughter, 6-year-old Mackenzie.

“I know that Ashleigh’s in good hands,” said Gwin, 35, who arrived in Iraq in April.

For tens of thousands of military personnel deployed in Iraq and Afghanistan, balancing military and family obligations is tough, but for families such as the Gwins with a severely sick child, it can be excruciating.

Krabbe (pronounced krahb-AY) disease affects about 200 babies a year. It keeps children from producing myelin, a protective covering around the nerves and brain, without which the nerves are raw and eventually die. Children who aren’t treated become irritable, stiff, can’t sit up or walk, and eventually become blind and deaf, then die within two to three years.

Ashleigh had a cord blood transplant, but because she wasn’t diagnosed and transplanted until months after birth, severe damage already had been done. Before leaving for Iraq, the Gwins discussed what they wanted to do if her condition worsened, including deciding not to put her on a ventilator simply so Howard could return to say goodbye.

“He feels that she knows that he loves her. He said goodbye but hopefully it’s not a final goodbye,” said Michelle Gwin, 34.

Michelle Gwin tries not to think about what could happen to her husband, who was very involved in caring for Ashleigh. One benefit of his military service is health insurance that covers many of Ashleigh’s needs not paid for by private insurance.

Last summer, when he first heard that his unit might be sent to Iraq, the Gwins discussed whether he should push to be left off the mission because of Ashleigh’s condition. There were no guarantees that he wouldn’t be tapped in the future for another mission. And if he went this time, he’d be able to serve with soldiers he’d trained with for years instead of being with troops he didn’t know.

“Michelle and I both felt that this was the right time,” he said.