Acting on a tip-off that a nine-year-old girl was being tortured by a family residing at Pataliputra Nagar in suburban Oshiwara, the police swung into action and rescued her on Saturday.
Subsequently, the woman who had employed her as maid was arrested, senior police inspector Subhash Vele said.
"During preliminary investigation, we found bruises on the girl's body. She has now been sent to Dongri children's rehabilitation home," Vele said.
The accused woman's daughter, who also allegedly tortured the minor girl, is at large, he said, adding that a search was on for her.
"The woman is in police custody and we are trying to ascertain the whereabouts of the girl's parents as she is unable to give any concrete information," said Vele.
The accused has been booked under sections 323 (voluntarily causing hurt), 324, 334, 370 (buying or disposing of any person as a slave) and 374 (unlawful compulsory labour), police added.