The incident, involving a black Volkswagen Polo, happened on King Street, Brynmawr, at about 00:25 BST.
The victim, named by Gwent Police as Sophie Brimble from Crickhowell, Powys, died at the scene.
A 24-year-old man was seriously injured and is being treated at Cardiff's University Hospital of Wales.
A 20-year-old woman has died following a crash in Blaenau Gwent during the early hours of Wednesday.