BC Ferries spokeswoman Deborah Marshall said the woman was driving down the ramp to board one of the ferries around 5:30 p.m. PT when her vehicle went through the wooden railing and plunged to the rocks below.
The vehicle did not land in the water, Marshall said.
A doctor at the scene confirmed the woman's injuries were not life-threatening and the local fire crew managed to remove her from the vehicle around 6:30 p.m.
The woman was transported on a stretcher to an air ambulance and flown to Victoria General Hospital for treatment. She was the sole occupant of the vehicle.
Her name has not been released.
Mayne Island is in the Gulf Islands just west of Vancouver.