If a player/team is use to seeing good pitching, this will be a challenge for any age level. Biggest thing is for them to trust their hands. They might have to swing much later after their lead foot plants. The best drill I know is actually using tennis balls during batting practice. With the tennis balls, pitch them so cross the plate after one bounce. You can bounce them at different speeds and in and off the plate. Have the girls hit them no matter where they are pitched. Even if they have to move their feet and entire bodies to get to the pitch to hit it. This teaches them to really focus on tracking the ball and being athletic. This is a good drill for any ball player. I always preach, when you are in the batters box, swing hard, make adjustments to win the battle. In the box is not the time to worry about your mechanics.