Ashdeep Kaur had moved to Queens here from India just three months ago and lived in an apartment in with her father Sukhjinder Singh and her stepmother Arjun Samdhi Pardas.
Kaur was found dead in her house's bathtub Friday, with police describing her death as "suspicious" after the body was found naked and with bruises.
A neighbour who shared part of Singh's house - including the bathroom - called him at work and told him that Pardas and his daughter had gone into the bathroom together.
The neighbour said Kaur had been in the locked bathroom for three or four hours and she had called the police.
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Police were on the look-out for Pardas, who was tracked down at a separate address in Queens.
She is being questioned by the police.
The New York Post quoted sources as saying that Pardas was supposed to have been watching Kaur and is a "person of interest" in the death.
Kaur was pronounced dead at the scene by emergency responders.
"When I heard what happened, I couldn't believe it," said neighbor Nancy Fong in the New York Post report.
Singh rushed home from work when authorities contacted him, and could be heard screaming in the back of an ambulance.
"He just moved [here] a couple of weeks ago," said Harmeet Singh, who works with the bereaved father at a chicken restaurant.
Mandinna Singh, a cousin of Kaur's father, said of the girl in a report in New York Daily News, "There was no water, but she was in the tub."
The little one said she (the stepmom) sometimes beat her.