Other psychologists say that having another child so quickly after such a tragic loss can compound the devastation, leaving the grief process unresolved. The pain felt by bereaving parents is one of the most intense of all sorrows and the most complicated.
"In Western culture, all feelings of hope and meaning and expectations are projected on to the child," said Therese Rando, a Rhode Island psychologist who wrote, "How to Go on Living When Someone You Love Dies"
Overcoming that grief can be difficult, especially if parents remember times they were angry with the child.
"When we lose a child, we feel our expectations are violated," said Rando.
"It's like losing a lung, it's so central," she said. "There is more guilt, more anger and more shattered pain, and other people in society are terrified of you because if it can happen to your child, it can happen to mine."
As the child's protector, we have "basically failed at the task" if a child dies, according to Rando. "We are assaulted. There is a sense of powerlessness and inability to carry out our role as parents."
Having another child after the "work of grieving" is over, can be a good idea, but not to replace the loss.
"The new pregnancy should not be an attempt to deal with the sadness," she said. "They will see this new little person as a distinct member of their family."
Hance said that she had her tubes tied after having her third child, but decided to do IVF after a doctor offered the procedure after hearing her story.
She said her daughters came to her in a dream: "I was standing in heaven and I could see Emma, Alyson, and Katie through these big gates. God would not let me inside the gates. He said that I had been given a gift from that doctor and I had to use his gift before I could be with my babies."
Dr. Richard Paulson, director USC Fertility in Los Angeles, said that having another child can sometimes fulfill the dreams of a complete family.
"It's not a replacement child, it's a reconstituted family," said "Because that person is gone, you don't replace that person," he said.
Paulson said he had worked with many patients seeking another pregnancy after the death of a child.
"People variously go through the grieving process and try to figure things out," he said. "It's fair to wait a reasonable amount of time, at least a year, and as the grief passes and you learn to live with the fact the person is gone, you can start looking forward."
Complicating Hance's grief is the fact that the woman who is responsible for her daughters' deaths is her sister-in-law, a woman she considered "the most responsible person I knew."
She said the accident has torn their family apart. Hance has been unable to even speak to her nephew Bryan, who was the last person to see the girls alive.
"I want to reach out and hug him and at the same time try to shake answers out of him, answers he doesn't have," she writes. "So for now, I stay away."
The Hances refused to participate in the making of the documentary by Oscar-nominated filmmaker Liz Garbus, which portrays Schuler as a "super mom" who rarely drank.
Schuler's husband, Daniel, cooperated with documentary producers and has contended all along -- despite lawsuits from the families of the adult crash victims -- that his wife may have had a stroke or other medical complicating factor to cause the accident.
Hance still struggles with allowing her children to go on the camping trip with their relatives.
"People always ask how I feel about Diane," writes Hance. "You can't imagine how complex that question is. How does a person go from being like a sister to me -- adored by my girls and cherished by my husband -- to being the one who ruined our lives?"