I recommend Lance Schmidt (on Massillon Rd, just east of I-77, 330-352-2660), who has been effective with my daughter. Lance also has proven success with his daughter, who earned a scholarship at Marshall.
Before working with Lance, my daughter (who is a lefty) was a good contact hitter but got into a rut of routinely hitting weak grounders toward 3rd/SS. I have seen vast improvement after only 2 sessions with Lance. She is developing the ability to hit the ball with authority to all fields and to consistently hit "rising" line drives. This has created more self confidence and re-ignited her passion to practice and play!
He breaks the skill of hitting into three steps and (what I think is most valuable of all) he teaches the girls how to "coach" themselves (identify and make their own adjustments). To re-enforce the mechanics he teaches and to help the girls develop solid muscle memory, he provides simple drills that can be done at home between sessions. In addition to all of that, he also teaches the girls to think at the plate (ie, hit the ball where it is pitched, have a plan at the plate, etc.). Wonderful stuff!