Williams-Paisley told ABC's "Nightline" in an interview to air Wednesday a woman calling herself Carrie contacted her by email and said her daughter Claire, a huge fan of the actress and her husband, was dying of neuroblastoma, a type of pediatric cancer.
"She said that her daughter had begged her to get in touch with me," ABC News quoted Williams-Paisley as saying in a preview story posted on its website.
"But she wasn't dying to get a hold of me. You know, that was kind of the beginning of the manipulation."
The actress said she and the woman exchanged dozens of emails, phone calls and text messages during the next 10 days. Carrie also sent Williams-Paisley photographs of Claire, images of journal entries and recordings of songs the child had supposedly sung for the actress.
Williams-Paisley's country star husband sang "Amazing Grace" to the girl on the phone, as well.
"You're singing to someone's dying kid," Paisley said on "Nightline." "And in the middle of it, there's no way that's not real. How can that not be real?"
But the couple said they began to suspect all was not what it seemed when Carrie said Claire died, then refused to give the Paisleys an address where they could send flowers for the funeral.
Carrie then also emailed Williams-Paisley, saying: "I don't need you to pray for me. Doesn't seem like God hears much of anything these days."
"I had a physical reaction," Williams-Paisley said. "Every red flag went up that I couldn't ask a simple question."
The couple said they later learned the photos of the fictitious Claire had been taken from the blog of a Southern California girl who is really suffering from neuroblastoma.
"That's the sickest part about this to me," Paisley said. "That is the part that when I start to talk about that, that's when I get really mad. That there were real kids, that there were real photos involved."
The ABC News preview piece did not say if the couple now know the true identity of the woman who scammed them or whether they contacted the authorities regarding the incident.