kat - my DD did that exact same type of drill. Actually, she kept a "pitching diary" (we still have it somewhere) where she charted her accuracy in practices, jotted notes about what she felt she needed to work on, etc. She kept this diary in her bag, and took it to practices, games and lessons. Each time she saw her instructor, they would review her notes, and prioritize things to work on in her lesson. That kept things moving, and she was working on trouble spots instead of repeating the things she was already good at. She was doing this at 12, so it gave her a sense that she was responsible for her success. We would take her to lessons, but SHE would interact and talk with her instructor, and mom and dad just listened and observed.
sports - I asked my DD what she used for drills. Other than what I said above, she more or less said it wasn't one specific drill, but rather a culmination of all the mechanics, practices, and learning from her mistakes with minor corrections. Slightly changing release points, slightly adjusting stride length. No two pitchers do things exactly alike. They have to "feel" what they are doing and make adjustments. Lots of trial and error that comes with years of proper practice. I think simply building good practice habits over time does more good than a specific drill.
Unless your kid is an absolute stud, all she needs is a repeatable, WELL PLACED fastball and a deceiving change-up that she can throw for a strike when needed. That will easily take her through high school. Most kids even throw a peel drop without even realizing it.