So after a week and a half of work I can now walk up and pet Rima on the head without her getting defensive.
When I take her down to the arena for ground work I work her and then tie her to the wall while I work a second horse. This helps her learn to wait patiently and be around barn activities and work out any tendency to pull back when tied. I lead her around while tidying up the arena, too.
She can walk and trot a circle in both directions now, but I’m not asking her to canter yet as she is still braced and learning to balance herself at the trot.
When she braces she sometimes gets tangled up and tries to get away. In this picture she’s just spun around to try to get away. I’m bracing the rope on my hip in so it doesn’t get pulled out of my hand.
All in all she’s clearly got a good mind and she wants to understand. She’s listening. Bit by bit her old defensive habits will drop away and she’ll lose the anxiety and reactivity.
Many thanks to Bobbie for taking the pictures!