I was trying out some sitting trot today to communicate better with her when I half-halt with my seat. All of a sudden she was just there - the contact was just right - not too heavy but she wasn't avoiding the bit and curling up either, and her motion was supple and fluid, with a lot of engagement. It was like riding a different horse. There was a huge amount of energy there, but it wasn't ending up in my hands or in her wanting to race or getting agitated when she couldn't. There was a softness throughout her body, but animation and even fire as well.
We did a variety of exercises - lots of transitions - 3 strides walk, 3 strides trot, 4 strides walk, 4 strides trot, etc. After a little bit, she was really getting these well. We also did some spiral in and spiral out exercises, using inside leg to outside hand on the outwards movements and even a bit of leg yield. Then we did some leg yields down the quarter line to the rail and then back out again. Everything was excellent. She even did some lengthening of the trot into something approximating medium trot, without losing the tempo. The halt and backing were right there as well. I was delighted!
I'm not really certain why things were working so much better for her when I sit rather than posting. It likely has something to do with my hands, which often are a trouble point for me. Perhaps my hands are just quieter at the sitting trot, allowing her to find a soft contact. Or it could have been my posture. I don't know. But at least it's working, and I'll take that.