COLUMBIA, Tenn. >> A 15-year-old Tennessee girl who authorities say was kidnapped by her teacher had endured months of abuse at the hands of her mother, according to court documents, making her particularly vulnerable to an adult predator.

The mother is scheduled to appear in court next month and has pleaded not guilty to five counts of abuse and neglect involving several of her children. The girl’s father filed for divorce Monday, citing the alleged abuse. His daughter was found safe with her teacher last week at a cabin in a remote part of Northern California.

The girl’s father has said the 50-year-old teacher brainwashed his daughter. In divorce documents, he said the teacher used his position of authority to “prey upon her, groom her, and ultimately entice her into running away with him.”

The Associated Press is not naming the student or any family members because the teen is an alleged victim of a sex crime.

The teacher, Tad Cummins, faces federal charges of bringing a minor across state lines for sex and state charges of aggravated kidnapping and sexual contact with a minor. Cummins’ attorney has said the girl went with her teacher willingly, and was not forced, threatened or coerced.

School records showed the girl often relied on Cummins “like a friend and a counselor” when she became upset or anxious at school.

A history of abuse at home can make children particularly susceptible to manipulation disguised as help, said David Finkelhor, director of the Crimes Against Children Research Center at the University of New Hampshire.

“They’re very vulnerable to the grooming because this is an adult who seems to care about them and is interested in them, and that’s probably something they’re not getting elsewhere,” he said.

Authorities said the mother physically abused several of her children for about a year, beginning in November 2014. The teen’s father was living at home during that time, but the couple separated in November 2015 and the father took sole custody of the children, according to the divorce filing. The parents have been married for 30 years and have 10 children together, though only four of them are still minors.

The mother is accused of hitting her children until they bled, knocking a daughter unconscious with a wooden board and throwing a chair at another daughter, bruising her leg, court documents show. The mother also smacked a child in the head for injecting herself with her brother’s EpiPen.

The mother said she can’t comment about the case. Her attorney has asked for more detail on the allegations and access to the children’s social media accounts.

The mother has been ordered to stay away from the children, court records said.

The mother is alleged to have banged the 15-year-old’s head on a washer, and at another point, she threw the girl down basement steps and locked her inside, the documents said.

The children wrote letters to the Department of Children’s Services about the abuse before the mother was arrested, according to one of the teen’s relatives.

Department spokesman Rob Johnson said he could not comment on the case.

The girl’s relative said Cummins knew the girl had been abused and took advantage of that information.

“We have a 15-year-old girl with a 50-year-old man and he obviously used his power, his authority to, whether it’s groom her or convince her, to do certain things,” the girl’s sister-in-law said.

In January, another student reported seeing Cummins kissing the girl on the lips, setting off an investigation into their relationship. The teen and the teacher denied they had kissed, but the investigation found that the teen often relied on Cummins for support.

“She looks at him like a friend and a counselor who knows how to calm her down when she is experiencing anxiety,” school records said.

Cummins described the girl as “a really good friend” and told school officials that the girl did leave her other classes to come see him “when she needs someone to calm her down.”

School administrators told the girl that she needed to go to a school counselor for anxiety issues and ordered the health science teacher to stay away from her. Cummins disobeyed that order a week later and was suspended, the records said.

He wasn’t fired until about a month later — a day after the girl was reported missing March 13, when the case began to attract national attention.

Federal court documents alleged the teacher had been plotting his escape with the girl after their relationship was discovered and planned to take her to Mexico, possibly by boat.

Authorities credit the caretaker of the remote Northern California property for helping police find the girl. The caretaker will get a $10,000 reward on Friday.

Abused children are often exploited by teachers, coaches and other people in authority, but what makes the Tennessee case so unusual is that they left the area together, Finkelhor said.

Still, he said, there’s a reason there are laws protecting children from statutory rape or abuse by authority figures.

“And the reason why,” Finkelhor said, “is we want these people to be thinking about the welfare of children without having their own sexual gratification become part of the equation.”