I also noticed that you are very stiff, especially when asking for and riding the canter. One thing you might try (it worked for me) is to open up your hips, let your knees angle out a bit, and completely relax your entire lower body. Focus on riding her rhythm with nothing more than your core; your abdomen and lower back. Of course, start that at the walk and then work your way up to the trot and finally the lope. It takes a long time to break bad habits you develop in riding (believe me, I know
It looks like you're trying to brace with your legs to absorb her motion, putting too much weight on your feet. Have you done any no-stirrup work? If not, that might be a really good place to start. One thing I figured out the hard way is that if you keep most of your weight on your feet and you brace your knees, then you're going to get dumped every time they crow hop because your center of gravity is down around your knees...making you top-heavy and easy to topple. However, if you learn to keep your weight in your seat instead, then that's where your center of gravity is and makes things a lot easier to ride out.
Along with that, your upper body is tense, which isn't allowing you the fluidity you need in your shoulders and arms. It would be better if you could work on a loose rein to develop the feel you need, but that can be difficult when the horse
won't work well like that.
I don't know if something like this would be practical for you, but you might try riding her the way I ride my colts. Don't worry about a perfect circle and don't worry about rate. What I do is I leave the outside rein completely slack, ride with the inside hand only, and keep the inside rein shorter (but still some slack) so that when I pick up my hand, it turns them into a tighter circle. That is how I manage their speed; when they speed up, I'll tighten them down to smaller circles, when they slow down, I let them spiral back out to the bigger one.
One last thing, and I'm not certain as it may be her markings throwing me off, but she looks like she might be lacking muscle in her hind end and, if that's the case, she is likely lacking in her back too. How sure are you that your tack fits her well?
All in all, you look pretty darn good considering and don't get discouraged. I think all of us having problems in our riding that we are working to fix (heaven knows I do LOL), regardless of how long you've been riding.