Cao crashed into the Marris family's station wagon in his rented Ford Ranger near Moeraki on February 21 this year.
Ruby's parents, Tristan and Kimberley Marris, suffered serious injuries in the crash and her sisters, Georgia and Sophie, had moderate injuries.
In addition to the 18-month jail sentence, Cao was sentenced to nine months' jail -- to be served concurrently -- on each count of dangerous driving causing injury to the other four Marris family members as well as Cao's mother, who was a passenger in his rented vehicle.
He was ordered to pay $27,500 emotional harm reparation to the Marris family and further reparations of $34,390.