It is just before midnight and an 18-year-old girl is sitting in the gutter after her high school formal after-party.

The end-of-year celebration at a house in Auburn in Sydney's west has been shut down. The teen, from a Catholic school on the north shore, is eager for a lift home after several hours' drinking.

Ruhi Dagdanasar, 45, is accused of sexually assaulting a 18-year-old girl after her high school formal in western Sydney in November, 2016. Credit:Facebook

A car, with a man in his 30s behind the wheel, pulls up beside her and sparks up conversation.

The teen will later tell police the next thing she recalls is being in the passenger seat of his car and feeling the overwhelming effects of alcohol as they weaved through the streets of western Sydney.