It sounds as if that was when your problems started - your horse got the idea she could run along at her own speed, you'd have no collection so no way to produce useful energy that you could hold and release
Here are a couple of Youtube channels that you can find some interesting info on.
If she's rushing her fences you might find that going back to grid work will help - try working towards a line of bounce fences - only 2ft max where every other fence is actually a ground pole - makes the horses think about what they're doing. Also lots of twists and turns - avoid jumping single fences over and over again
This one is EventionTv, they have 43 videos at present
This one is from British Showjumping, they have 208 videos, a mix of instructional stuff and basic interest things like clips from competitions