When the girl was 5, she was brought to the United States on a tourist visa and was almost immediately put to work, according to the filing. She said she spoke no English at the time.

She would start working at 6:30 a.m. or 7 a.m. every day, cleaning, making beds, vacuuming, cooking and gardening, among other chores, and would continue until the Toure children went to bed, she told the authorities. Several unidentified witnesses confirmed seeing her perform such chores at various points from 2000 to 2016.

The authorities accused Mr. Toure and Ms. Cros-Toure of denying the girl the schooling, medical care and other opportunities they afforded their five children, some of whom were older than her. When asked about the girl, the couple would say that she was a niece and had finished high school, according to the filing.

Mr. Wyatt, the lawyer for Mr. Toure, and Scott Palmer, a lawyer for Ms. Cros-Toure, said that the family had good intentions, but that their efforts to help the woman were frustrated by her status as an undocumented immigrant.

“The intentions were to actually get her in school and to educate her, but then, once she was here, they needed the documentation to get her into school that they didn’t have,” Mr. Palmer said.

But the federal authorities painted a darker picture.

According to the April filing, Ms. Cros-Toure would physically abuse the girl, who had scars consistent with stories she told of being whipped with an electrical cord and having an earring ripped from her ear. The girl also said that she had visited a doctor only once and had slept on a floor for years, upgrading to a twin bed only when one of the children left for college.

In June 2016, she got into a fight with the couple and ran away, according to the filing. She spent a night with one of the unidentified witnesses, for whom she had previously worked as a babysitter. The witness called a friend who let the young woman stay with her for a week, but she then returned to the Toure household. She was forbidden to leave and considered suicide, she said.