My daughter' s PC gave her this drill to help with keeping your hips turned and it is easy to do inside. place a wiffle ball on the floor (the hallway works great for this). Stand with a hand towel so when you have your arm straight down it just touches the top of the ball which is centered between your feet. All you have to do is go through your pitching motion and when work to hit the wiffle ball down the hall. Follow through as you would pitching. If you do it right, the ball will travel on your powerline. You will have to adjust the ball a little to find the bottom of your circle but you will get the idea.
Also it looks as though you are giving (bending) your front leg a little too much when you deliver. Try doing one leg bounding to get the feel of firming that up. Simply, just start with you feet together and leap foward as far as you can. Just like how you would
pitch. As you get further out you will definitely feel the need for your front leg to be firmer.
do you possibly have video of the first drill?