"I feel like if she's got any chance at all to get out of the orphanage, it's the right thing to do," Horton said. "If Putin signs [the legislation], I don't know that there is hope left."
Horton, a research professor at George Washington University, adopted her daughter, Emma, about four years ago from a Russian orphanage.
She spent a week in February with the child she hopes will be her second daughter, and waited the better part of the year as Russian court hearings on the matter were continually postponed.
"I fell in love with her, as you do," Horton said. "These kids so desperately want good homes and someone to love. It's heartbreaking. It's so awful. I wake up in the middle of the night thinking about her and wondering if she is warm and well fed."
Horton and the Whaleys have worked with Adoptions Together, an agency with offices in Maryland, Virginia and Washington that conducts home studies, training and other services to facilitate international and domestic adoptions.
Janice Goldwater, founder and director of the nonprofit, said Adoptions Together was accredited by the Russian government to directly process adoptions until about two years ago, when working with the Russians became too difficult and too expensive. Over about 20 years, Adoptions Together placed about 1,000 Russian-born children with adopted parents in the region, she said.
Goldwater said she applauds the Russians for looking to strengthen their own domestic adoptions, but she fears Putin's action is politically motivated.
"My reaction is pure sadness," Goldwater said.
The U.S. State Department expressed "deep concern" over the potential ban.
"It is misguided to link the fate of children to unrelated political considerations," State Department spokesman Patrick Ventrell said in a statement. He said the United States was troubled by the restrictions the bill would impose on the ability of Russian civil society organizations to work with American partners.
Heather Whaley, a therapist who works with autistic children, said she knew Addie was meant to be part of her family as soon as she saw her photo on an adoption website about a year ago. She and her husband, an engineer, have been trying to raise enough money to finance the adoption, including petitioning help through their website, http://www.bringaddiehome.com.
"We are fighting for her; if I have to sell everything we have, I'll do it," Heather Whaley said. "I can't imagine what will happen to her.
"It is so difficult to face that reality that she might not come home."
Reuters contributed to this article.