Volunteer crew of the Mumbles lifeboat rushed to the scene at Limeslade Bay South Wales after a call was made to the UK Coastguard at Milford Haven saying a car had entered the water.
By the time two lifeboats arrived at the scene, the 37-year-old driver had managed to escape the vehicle, which ended up almost entirely submerged in water, and swim to shore.
The woman, who is seen in shocking video stood in front of the vehicle on the edge of the water, was taken to hospital by ambulance.
She was later detained under the Mental Health Act, according to South Wales Police.
Mumbles Lifeboat official Richie Webborn, who rescued the woman, said: “There wasn’t much to identify the location other than a small amount of debris which lead a trail to the bottom of the cliff just below Fortes Ice cream parlour.”
Rhossili coastguard wrote on Facebook: “At 6am this morning Rhossili Coastguards were tasked to Limeslade in Mumbles where a car had gone over the cliff with a person in it.
“As we set off from station we were informed that Mumbles coastguards and Mumbles RNLI were both on scene, we were then notified the lady that was driving the car had managed to get out of the car and was in the water.
“She managed to get to the cliffs and made her way up the bank to waiting police, coastguards and ambulance. We arrived on scene.
“The casualty was being examined by ambulance crew, she was asked if anyone else was in the car.
“As there wasn’t anyone else and the lady was OK and on the way to hospital.“