Maachil - My DD sometimes struggles with a top hand chopping motion, especially if she's late on a swing. She's neither learning disabled (4.0 gifted identified student) or receives poor instruction (sees one of the top hitting coaches around weekly). I think she might just have a future in the game, too, but I could be wrong. It's never too late to make changes to a swing to improve. Jose Bautista completely made over his swing in his late 20's to become one of the best hitters in the game - he had just a little bit of success beyond the rec level.
A couple of things we worked on with DD -
Approach. A hitter needs a "Yes, Yes, Yes" or "Yes, Yes, No" mindset. Every pitch is a strike until the last moment when the decision is made NOT to swing. The hitter doesn't decide to swing but rather not to swing. The decision to swing is made before the pitch is ever delivered. This will help her get on time which by itself may help with the chopping motion. Look up Matt Lisle on the web. He is the hitting coach at South Carolina and an online hitting coach. This is straight from him and he has some good free stuff you can look at on approach.
Getting work on the tee is great advice. I'd recommend a particular drill which we call the Angle Drill. Other call it the Stretch and Fire Drill. Look up Casey SNF 2013 on YouTube for a great example of this drill. Really concentrate on getting the back elbow in the slot on this drill to keep it from being choppy. I'd also work on some one handed drills with both hands using a small t-ball bat or one handed bat to concentrate on the proper hand path.
Hope that helps. Good luck to you and your DD!