Let's talk about taking steps back to go forward. I think a lot of times in training, people get stuck because they have a goal (in Bottle's case, the basics of lightness and roundness), and they only want to work in a linear path towards that goal. But training isn't linear. Sometimes you have to take a step back, or work around a problem rather than ramming into it head on.
A lot of people would look at the difference between photos one and two and think "Erin, what the heck are you doing?! You've made that horse hollow and upside down!!" And yes - I did. However, it was for a purpose. Bottle has a very downhill natural balance, and when carrying a rider she has a tendency to want to lean on the reins to support herself, no matter how long you make your reins, she will find that extent and hang on your hands. Me holding her up will never ever teach her to properly use her hind end. So we progressed to photo two. Here I was using lateral work and lots of bending to lighten her on the reins. If she has to hollow to do that, so be it. I HAD to get her to hold her own head up before I could work on bringing the haunch under, otherwise I'd just be doing all the work for her. (Note: this process involved no bitting up whatsoever). Finally, when she was light to basic rein cues, I could work on asking the hind end to come under the space we had freed up, and we got photo three - the very beginnings of uphill movement.
The moral of the story is that training doesn't always have to be "pretty". Sometimes, things have to get "worse" before they get better, especially when you're unwinding issues from a horse's past, or working to break habits. I hope this makes sense, and feel free to ask questions below!