She is in a large family, younger than the last sibling by seven years, "so there is no one she can hurt," said Gertz.
The mother has fostered 150 children and has a teenage son with FASD.
"We are told [Ellie] is incredibly argumentative but not having the violent outbursts she was," said Gertz. "I couldn't be someone who could emotionally withdraw from her. This mother is experienced and comes into this with a new energy. I was beaten up and pushed down."
Gertz said her heart aches for Ellie, even though her daughter was more loving toward the "insignificant people" in her life than her family. "She would smile better at someone in the grocery store," she said.
Now, 5-year-old Talia and 11-year-old Jonah are blossoming. For the first time they are the focus of their parents' attention. The entire family is in grief therapy.
Gertz said she still has nightmares and constantly second-guesses her decision to let go of Ellie. But her husband's response is, "What about the rest of the family?"
"The other children were compromised," she said. "We had three birds in our nest, not one."
"I have come to accept that while she was very much my daughter, I was never her mother," said Gertz. "She never bonded with me. That's a hard pill to swallow."
"I couldn't be the kind of parent of my dreams," she said. "I could face the trauma, but I couldn't soothe the one I loved so deeply."
ABC News research specialist Nicholas Tucker contributed to this report.