Sister Nora Ashe, a school teacher at St. Joseph's High School in Brooklyn, was the rear-seat passenger on the car, a 2002 Mercury Sable.
The accident happened at 1:40 p.m. on Monday along Woodbridge Avenue in Edison.
Sister Ashe was pronounced dead at the scene.
Her sibling, who was the driver of the car, was taken to Robert Wood Johnson University Hospital in New Brunswick. Kathleen Windram, 63, of Paramus, was listed in stable condition.
The front-seat passenger, Patricia Ashe, 70, of Edison also was taken to the hospital. She is listed in critical condition.
A preliminary investigation determined the box truck rear-ended the car, officials said.
The investigation is continuing. No charges have been filed.