Having not yet watched the videos, but read all the comments and agreeing with most of them I will add: why go at a speed that you/she are/is not ready for yet? Assuming it's not pain, which of course would be the first thing to deal with.
Ensure that the brakes work 100% on the ground at a walk and trot. Every time. No crowding.
Then mount and ensure the brakes work at a walk. Every time. When you say stop, she stops NOW, not three strides from now. If she doesn't stop on the spot, back her up to where she was supposed to stop, plus a step.
Then move to trot. Trot, walk, stop, walk, stop, walk, trot, walk, stop -- repeat ad nauseum. Again, she MUST stop where you want her to every time. No excuses. No leniency. Once that is clear, move to walk, trot, stop, skipping the walk between the trot and stop.
Weeks or months from now, then move to the lope. Doing anything sooner is 1. Dangerous 2. Probably confusing.
This might take a WHOLE lot of patience and ignoring the "I wanna" in your mind, but doing things too fast is not doing things right.