SAS flight SK2322, a Boeing 737-500, was approaching Kristiansund. Passengers were briefed to fasten seatbelt when passing through FL110. SK 2322 was cleared descent to 5000 feet, to expect a visual approach to RWY25. In clouds, descending through 7000 feet they experienced moderate to severe turbulence for a few seconds. Considering the weather, the flight crew had not expected this kind of turbulence. Passengers were briefed about the turbulence and when contacting the cabin crew she told the flight crew that she was hurt and sitting down ready for landing. After landing, cabin crew remained seated while the passengers were disembarked by the co-pilot. An ambulance was requested, and the cabin crew was transferred to the hospital in Kristiansund.