Amazing session with Beth (but my abs are tired)

I had my third (?) dual pilates and riding session with Beth today.  This one had a breakthrough!
I really get a lot out of the dual sessions because Beth has seen me often enough now that she works on the current issue inside, so I can feel it without having to think about riding - and then she gives me exercises for continuing to improve at home.
Then we work on the same thing on Charlie, which helps me feel how changing my alignment can really change how Charlie can move.
Today we worked on my upper back, which has to do with pinching my shoulder blades together, and not rolling my shoulders back.  We did quite a few exercises and they were surprisingly hard to do.  The right shoulder in particular is reluctant to move.  Using my lats, instead of my shoulders, was also quite hard.  The at home exercises are to do quadriped on a ball and to do scarecrow on the ball and then lift my arms at the end.
Then we did some work with Charlie at the sitting trot.  This ended up being genius.  Without messing around with the angle I create at the posting trot, I could focus on lining up the two plates - the lower abs, which need to come forward (tuck my butt under me); and my shoulders, which also need to come forward, but not until after they pinch back.  I feel like I am tilting forward with the shoulders, but once everything lines up, I quit being behind Charlie's motion and I feel completely solid and planted.
Then the next big thing to work on was to loosen my legs.  I tend to grip with them, particularly after a down transition.  When I consciously loosen them, I sink deeper into the saddle and have much better feel.
With loose legs, I could then think "up" and control the rhthym and increase the bounce.  It was actually kind of a miracle how much I could do with the tucked under butt - all coming from the abs, not the butt itself.  Using my butt actually defeats the progress.
I had a hard time with opening my fingers.  As we go, and particularly for up transitions, I loosen my fingers which doesn't help Charlie at all.  I need to pay a lot more attention to this because I don't notice I'm doing it.
Then we worked on canter both directions, getting an active walk where Charlie's shoulders lifted and I could feel either a halt or trot at any step.  Then we would trot, trot a 10 meter circle, and canter leaving the 10 meter circle.  We went out to a 20 meter circle, and then interestingly, when we made the circle more like 15 meter circle, to the right Charlie just fell apart.  For now, I'm going to assume that's coming from me, but it was a huge difference in his ability to hold that canter on the left and right side (I also had to ride him counterbent, so that's one of many reasons I assume it is me preventing him from doing them equally).
I got a longer whip after using Beth's, and I'm going to start riding him with my little spurs.  He's ignoring my aids again, which I know is my own fault, but I need to break that habit so we can work on cooler things.
It was a great lesson.  I felt like I started to feel how to use my core, and that will help motivate me to stay on top of the mat exercises at home too.
There were like 100 other tips and steps, but my brain is full from trying to feel it all so that I can work on it before next time.  This has been so helpful for me.