Gwent Police confirmed Courtney Smith from Pontypool, Torfaen, had died following Wednesday's incident on Belmont Hill, Caerleon just after 23:00 GMT.
She was being treated at Newport's Royal Gwent Hospital. A 21-year-old Thomas Lawrence from Caerleon was pronounced dead at the scene.
Anyone with information has been asked to call police on 101.
A 16-year-old girl has died days after a crash killed a man in Newport.