I see this all the time with our 16U Gold girls. Much tougher to hit the long vertical axis than lateral. In fact, the pitchers these D1 prospects find the most difficult to hit hard (not necessarily just getting the bat on the ball) are the girls who have mastered the peel drop. A good one can literally tell the girl up to bat that she is going to throw three in a row and a good hitter won't be able to do much with it if the pitcher can spot it well. Lots of groundouts and a few strikeouts, the Ks coming when a girl gets behind early and has to swing at one out of the zone.IMO, and in accordance with what DDs PC teaches her, it's probably best to master the fastball and change up before adding other pitches to the arsenal. If you can't spot those two, it's unlikely you can spot a screwball.
A good, former DI catcher/batter recently told me she thought it was harder for her and her opponents to hit the drop/riseball combo than the curve/screw combo because the former requires a longer vertical axis through the strike zone than the latter. She said generally as a batter, she felt that she and opponents could make the lateral adjustment better than the vertical.