Police are appealing for witnesses to the collision, which took place in London Road, near to the Belvedere Arms, at about 7.30pm.
A blue Mercedes SLK 320, which was overtaking, struck a green BMW 323i, which was travelling in the opposite direction.
Three occupants of the cars, including both drivers, sustained minor injuries and were taken to Frimley Park Hospital.
A 68 year-old woman, a passenger in the BMW, sustained serious chest injuries.
Anyone with information can contact PC Chris Howlett, from the roads policing team in Taplow, via 101. To remain anonymous, call Crimestoppers on 0800 555 111.