Rinoa wasn't always a sorceress. She became a sorceress when Edea somehow lost her powers and they were given to Rinoa. If I remember correctly, Rinoa was in the process of giving the Odine Bangle to Edea and Edea destroyed it and knocked Rinoa to the back of the room, lifted her in the air with her magic, and then it looked like she was "punched" in the face.