Hilt and her husband adopted Nina from Russia in 2004. Nina was the second child they'd adopted from Europe and Hilt said from the beginning she was withdrawn and often impossible to handle.
"She would bang her head on the wall, she would pull her hair out if something frustrated her," she told "20/20."
A stay-at-home mom, Hilt says she began drinking heavily in secret, downing close to a 12 pack of beer each day. The alcohol made her even more impatient with her children, as it did on the day when she finally lost patience with Nina.
"Nina picked up a fork off the table and went towards [her sister] with it, and I saw red," Hilt said. "I grabbed her and I snapped. I hurt her. I didn't mean to hurt her. Then I kicked her with the side of my foot and told her to get up and then I put her up in her bed and struck her repeatedly."
Two days later, Nina died from internal bleeding. Hilt admitted that what she did was inexcusable, but says she had never heard of RAD and didn't know that help was available to her. She said she's sharing her story hoping that no other woman has to walk in her shoes.
Across the country, at the edge of Glacier National Park in Montana, Joyce Sterkel understands the despair that many adoptive parents and children feel. She raised three Russian-born teens, one of them a boy who had tried to poison his first adoptive mother.
She has dedicated her life to preventing American parents from disrupting their adoptions.
"It's like a divorce, with all the ramifications of a divorce," she said. "Legal, spiritual, emotional, financial -- it's a divorce. I think these parents are just hurt people that are afraid for their lives. I am the last person to judge them because I have seen children that, for lack of a better word, truly are sociopaths."
In 1999, Sterkel opened the Ranch for Kids, a last stop for parents who can no longer handle their adoptees and are considering giving them up. It can house 40 kids at a time and is at capacity with a long waiting list.
"It's really sad because many times the parents are at the end of their rope and they're crying on the other end of the phone, 'Please help!'" Sterkel said.
Though she's a nurse and not a trained psychologist, Sterkel has an uncanny ability to reach these emotionally damaged children.
"I'm very honest with them," she said. "And I'm straightforward and sometimes very blunt."
The Mulligans, seeking help to avoid disrupting their adoption, spent several months consulting with Sterkel on how to deal with Margarita and Slater.
"I still feel that there's a soul in there that can be salvaged, a heart that can be saved," Tanya Mulligan said.
Sterkel suggested that all three Mulligan children -- even the seemingly unaffected Elena -- should visit the ranch. So this summer "20/20" flew them to Montana to stay at the ranch for a week.
The Ranch for Kids is all about structure and obeying the rules. Every morning, the kids line up for a bare-bones breakfast and then head to their chores and classes. Some kids are on laundry duty while others muck-out horse stalls. A school on campus allows the kids to keep up with their studies.
Sterkel is no-nonsense when it comes to disciplining both the parents and the kids.