The 31-year-old woman said she was carrying her nephew in one arm and a cat carrier in the other after a visit to the veterinarian.
The victim's son says video shows the caregiver climbing into bed with his mother before leaving the house.
The 85-year-old woman was discovered unconscious and unresponsive in the home early Monday morning.
Police say that a dispute over the movement speed of the checkout line led to 25-year-old Amber Thompson allegedly threatening to harm a woman "outside."
Police said the stabbing was the result of a domestic dispute.
Police responded to the scene on Crotona Parkway near East Tremont just before 1 a.m. for reports of an assault in progress.