Castro clung to home, never wanting to leave for more than a day, even to visit Gregg out of state when she lived with her family in Indiana.
"He was adamant in the fact that he wanted to leave home early morning and he had to be back by evening," Gregg said.
Her family often made travel plans with Castro that they then had to cancel because of her father's obsession with his own four walls.
Gregg said she never saw signs of the 6-year-old at her father's house and that she never saw her with him. But about two months ago, he showed her a picture in his cellphone.
Gregg asked who it was.
Her father told her that the girl was his girlfriend's child by somebody else.
"I figured at the most he had an illegitimate child out there, you know, and I would find out eventually," Gregg said.
She asked him to get a paternity test. She wanted to know if she had another sister out there somewhere.
Now she knows that she does.
Gregg recalled fond memories of growing up in the house and fun times with her father. He lined up the children in the backyard and trimmed their bangs himself, she said. He took her for rides on his motorcycle.
And he never abused her, she said, or her sisters, as far as she knows.
But he beat their mother, Grimilda Figueroa, whom he accused of fooling around with neighbors. He was very jealous, Gregg said.
"When mom and dad were fighting, it's like I just wanted to melt into the ground," she said. "I've seen him basically stomp on her like she was a man," Gregg remembered.
Then after a bludgeoning, her mother had enough, and the family split up. The other children left with her mother, but Gregg stuck by Castro, believing the excuses he made for the violence. She finished growing up under his roof, she said.
A daughter divorced
Gregg is through believing in her father and is appalled at the extent of his alleged deception and cruelty.
"To go to the vigils, to show these girls the footage of their parents' pleas for their return, to rape, starve and beat innocent human beings ... I am disgusted."
Gregg wants the girls who suffered in captivity to get the treatment they need, recover as well as they can and have the best lives possible. It was the first thing she mentioned during the interview.
She is relieved to see them and the little girl, her new sister, return to their families.
She hopes they can understand her father's actions are not a reflection on her family.
"We don't have monster in our blood," she said.
Gregg's mother died in 2012 after a bout with brain cancer. Now she has lost her father, too. She still cries for her mother, she said.
"I don't cry for him."