I think you ride very well. One of the better Western riders I have seen post on this forum. Your horse is a very nice mover and has a correct lope and good jog. Don't mess it up by slowing her too much .
She's a doll!
You just need those stirrups down. Your posting was actually not bad. You moved in rythm with the horse, which has a slightly choppy rapid stride at trotting out, and that's what is important. I didn't see you bopping the saddle at all, in fact the horse looked pretty happy and comfortable with you on her. You seem to have a very trusting relationahip.
The ONLY thing you really need to work on, already mentioned, was the overtwisting of the upper body. You ride so quietly overall (a little too noticeaqble spur work , keep it lower and try for ankle movement only) so you need to quiet the upper body in that lateral work.
I could not ride half as nicely as you do, and that's the plain truth.
I totally I agree with tinyliny on this one, other than the end part as I obviously haven't seen her ride! ;)
You do seem like a very quiet rider, and your horse has the word "willing" written all over her. She's responds quietly to your aids and looks to have a lot of 'try'!
Again, as others have said, having your stirrups lower will make it easier for you to make the spur cues subtler, as well as you will be able to easily as with leg before resorting to the spur. I think putting them down will also completely correct your posting, as it seems like you obviously know HOW to post, its just the awkward stirrup length is making it a little wonky.
Like someone else has already mentioned, when you twist your body to watch her hip, you are shifting your weight. Now, you obviously also know that your seat is an important aid (as I saw you sit deeper for slowing the gaits/stops, etc.) so did you not also realize that you shifting your weight so drastically could also be sending her mixed signals?
Just something to think about.. :)
Great job though, I'm glad to see some of the awesome western riders on this forum!