I actually watched a few of her reining videos. It amazed me that she did not get much better at all in a years time. It also somewhat surprised me that she seems to have an issue with the fast/slow transitions and doing it seamlessly at the right time. Obviously these were other things, but that one from MY beginner perspective, would seem to be the easiest for a rider of her level. Perhaps not?
People for what ever reason seem to think reining is easy. They seem to think it just about getting on a horse and running a pattern. Thing is that it is so much more then that and the horse especially the well trained well tuned ones are quite hard to ride. People seem to think that you can take a finished reiner and just clime on and run a pattern and win. I have seen this quite a few times. People go out and buy a NRHA Open World Champion horse and think they are going to clean up in the Rookie classes and win Rookie of the year. Never seems to work that way.
Oh, I am so well aware of that reiner, but at least for me the speed adjustments are the easiest. I would think for a rider of her level that would be the simplest. It is very difficult to get correct plus speed in spin, back, etc. And once your horse is stepping in the back....SO hard to fix. And one of the videos had that horse really stepping around, rather than the pivot on the inside rear. Stops improved greatly-will say that for her!
The movement in the rear on the turns is the way she is riding the horse more then the horse. Since she is a Dressage rider they do not pivot like a reiner does. So I would think that would be hard for her to get and even harder for her to feel what is correct. Being that it is so different then what she is use to.