Hmmm, three mechanical things. Let me ask the question no one has asked yet? What's your goal? Is it to develop a top-notch pitcher, to increase a good pitcher's speed, or help a beginner get the ball over the plate. My answer would change depending on your goal.
If it's get the ball over the plate, I would choose:
1. Go straight down the power line
2. Get open
3. Keep the arm circle on the power line.
Do those three and the ball should go where you want it. Can't guarantee it will get there fast, but it should be accurate.
If you want to develop more speed, my choices would be:
1. Stronger drive with legs
2. Relaxed arm with whip at the end (IR is a part of that; I'm not cheating, really)
3. Throw hard (seems like a given but it's often not); I'd accomplish it by teaching her to pull the upper arm down hard with the back muscles, then pull the hand through with the forearm muscles
If you want to develop a top-notch pitcher, depends on what she's not doing out of those two lists already.