Authorities said an autopsy of Marchella Pierce, weighing just 15 pounds when she died Thursday, was inconclusive, the New York Daily News reported.
Police sources said the child had bruises on her ankles that suggested she could have been tied to her bed, the newspaper reported.
Carlotta Brett-Pierce, 30, of Brooklyn, could face a murder charge if the girl's death is ruled a homicide after further testing, the sources said.
Brett-Pierce had told authorities the bruises were from a fall.
Neighbors of Brett-Pierce, who had petitioned the city Housing Authority to have her and her mother evicted from their apartment complex, say her arrest did not surprise them.
"All they would do was go out and buy drugs. Crack. You could smell it. They fought with a lot of people," Elizabeth Soto, a resident of the complex, told the New York Post. "The way they were living in that apartment, they would open that door and you'd get sick."
In addition to the charges of assault, reckless endangerment and endangering the welfare of a child, Brett-Pierce was charged with drug possession after small amounts of crack cocaine and marijuana were found in her apartment.