The incident took place along the A27 westbound at about 6.50am.
She is believed to have been travelling in a 4x4 jeep, towing a caravan, when the vehicle lost control and collided with trees on the embankment off the road.
Paramedics were first to arrive at the scene.
They called on the assistance of firefighters from West Sussex Fire and Rescue to free the trapped woman, understood to be in her 60s, from the wreckage.
Crews from Worthing and Littlehampton arrived at 7.02am, accompanied by a heavy rescue tender from Worthing.
They used hydraulic cutting equipment to rescue the injured woman from the 4x4.
Firefighters also moved the caravan which had jackknifed across the carriageway.
Paramedics treated her at the scene, immobilising her for potential spinal injuries.
She also had a wound to her head and had suffered an arm injury – none of which were believed to be life-threatening, a spokesman from South East Coast Ambulance Service said.
She was taken to the Royal County Hospital, in Brighton for treatment.
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