The mother, 54-year-old Joanne Alvarez, first gave the girl Baby Motrin medicine. Officials say when that didn't work, Alvarez applied a fentanyl adult medical pain patch on the child's skin.
Police say the girl was found unconscious in her bed at around 3 p.m. She was rushed to Mount Sinai Hospital, where she was pronounced dead.
The autopsy on the young girl was inconclusive, pending toxicology results.
According to an official, Alvarez will be charged with second-degree manslaughter, criminally negligent homicide and endangering the welfare of a child.
Authorities say the patch was prescribed for Alvarez several months ago for an injury she received after an accident in 2000.
The label clearly stated to keep out of reach of children.
Law enforcement officals add a doctor at Mount Sinai told investigators the injuries are consistent with someone suffering from affects of fentanyl.
A fentanyl patch is applied to the skin and delivers drugs through the adult patient's skin and and into the bloodstream. It can relieve pain for up to three days from a single patch application.
Click here for more information on the fetanyl patch.