On October 2, a semi-trailer travelling east along the highway collided with a utility, also travelling east, at around 9.15am. The utility then collided with a sedan.
A 17-year-old girl, who was travelling as a passenger in the sedan, was pronounced deceased at the scene.
Two other people in the sedan, a 48-year-old man and a 44-year-old woman, were transported to hospitals in Brisbane where the woman died on October 8.
The driver and sole occupant of the utility, a 36-year-old man from Oakey, was transported to hospital for treatment.
The driver of the semi-trailer, a 35-year-old man from Victoria, was not physically injured.
Investigations by the Toowoomba Forensic Crash Unit are continuing.
If you have information for police, contact Policelink on 131 444