WA Police said the woman walked into the Bayswater police station this afternoon, and reported she had been struck by something in her upper body while driving with a man on Whatley Crescent.
Ambulance officers transported a 24-year-old woman from Yangebup to Royal Perth Hospital about 2:50pm this afternoon.
Her injuries are not believed to be life threatening.
The man was not injured.
WA Police said while the woman believed she had been injured by a firearm, they were working to establish the exact nature of the projectile.