Air carrier pilot reported while avoiding weather in cruise; they suddenly lost control of aircraft due to severe turbulence. One flight attendant suffered minor injuries.

Narrative

During cruise we were avoiding weather in the area. Light turbulence procedures were in effect. Navigating using our EFB; FMS; and onboard weather radar to avoid weather. ATC informed us of nothing worse than occasional moderate chop in the area. Suddenly we hit severe turbulence; loss of 200 ft and 10 kts; the event didn't last longer than 10 seconds. Immediately following the Captain called to check on the flight attendants and passengers and was informed that the number 1 flight attendant fell as a result of the turbulence. We informed ATC of the event and they later [provided priority handling] for us. After consulting with the Injured Flight attendant said she was okay to continue to destination; where she was later checked out by EMS. Aircraft was also written up as a result of the severe turbulence encounter.Cause: There was no indication of anything worse than occasional moderate turbulence in the area; the EFB showed light turbulence and never registered even registered our severe encounter.