There is pretty much always more than one reason why pitches go wild in one direction or another. Some are obvious and easy to spot, others not so much.

Here's one for pitches going high. Check to make sure that the pitcher is accelerating her arm circle at the right time. There can be a tendency sometimes for pitchers to wait too long to start accelerating their arm. Instead of speeding up from the top of the circle to the bottom, they wait until they hit the bottom of the circle, then start accelerating.

The phrase I like is get quicker earlier. In other words, start accelerating as soon as you pass the top. If you do that, and use a long, loose arm, you'll feel the proper release point at the bottom of the circle, and have the proper timing. It'll help you throw harder, too.