"Parenting is not something you can ever let go of, even if your children are gone," said Jackie Hance, 40, of Floral Park, New York.
Tests showed the 36-year-old Schuler from West Babylon, New York was drunk and high on marijuana at the time of the crash, which is the subject of an HBO documentary due to be aired later this month.
Hance talked publicly for the first time about the accident in an article published on Tuesday in Ladies' Home Journal, recalling the day she let her three daughters go on the family camping trip in upstate New York.
"I felt confident that they were safe, since my husband, Warren, and I had sent them away with my sister-in-law, the most responsible person I knew," she said.
She said she still hasn't come to terms with the revelations about Schuler's behavior.
"People always ask how I feel about Diane," she said. "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?" she said.
"How could this person I trusted completely have done something so unthinkable that I couldn't -- and still can't -- wrap my head around it?"
Hance said she is expecting her baby in the fall.
"After the accident so many people suggested that Warren and I consider having another child. They said having a baby was what the girls would want and it would give us a future," she said.
Schuler's 2-year-old daughter, Erin, died in the crash, as did Hance's daughters Emma, 8, Alyson, 7, and Kate, 5. Schuler's son, Bryan, 5, survived.
In the other car, Michael Bastardi Sr., his son Guy and family friend Daniel Longo, all of Yonkers, N.Y., died. Bastardi's surviving son Michael Bastardi Jr. told Reuters he read Hance's article.
"It definitely doesn't bring any closure to me, but I'm happy to see that Jackie Hance is able to talk about it," Bastardi said. "She said it's hard for her to move on and get the truth, and I want her to know that's exactly what we're trying to do too."
The Bastardi family filed a wrongful death lawsuit against Schuler's family and against Hance's husband because he owned the vehicle that Schuler was driving that day.
The Bastardi family put out a book about the crash last month called "Taconic Tragedy: A Son's Search for the Truth," available on Amazon.
On July 25, HBO will air a documentary called "There's Something Wrong with Aunt Diane." The Schuler family cooperated in the making of the film, which was produced by Moxie Firecracker and HBO and directed by Liz Garbus.
(This story was corrected in the last paragraph to show Schuler family cooperated in making of documentary but did not help produce it)