I haven’t read all of the replies, so forgive me if I’m repeating some things. First, though, I’m happy to see Steve Young being praised. He really is good at what he does.
I’ve raised a few babies in my day including my current 16-year-old gelding. He flung himself over backward in slow-motion when he was a yearling and first learning to lead (I bought him as a basically unhandled but friendly yearling colt). In his case, we were out in his turnout pasture and it was nice, soft grass, but he bonked his head enough when he landed that when he went to right himself he kind of laid there for a minute and shook his head like “What just happened??” If he had been a cartoon character (and he’s close!) he would have had little stars and birds circling his head.
He never pulled back again until trailer loading started. He bonked his head on the top of the trailer (wearing a head-bumper thank goodness) and that was all it took. Never did that again.
But some horses aren’t that easy, and they can seriously injure or kill themselves with such shenanigans (not to mention the people around them).
I’d do something like a blocker tie-ring. I’d put her in a bedded stall, maybe with a head-bumper on, NON-breakaway halter, and I’d start with the blocker tie-ring. She should be able to get enough slack from it that it won’t give her the resistance she’d need to fight and flip. Eventually, she’ll figure out that pulling back will get her nowhere.
I’d work with her on giving to pressure (the way Steve Young does…asking her to lower her head when she feels the pressure at her poll) every single day. And when she’s getting her feet done or anything else that might make her feel trapped, right now she needs to be allowed to retreat (take a foot away or step back if it’s obvious she’s going to escalate) without any resistance. Walk with her, don’t give her a chance to pull, and when she’s quiet again, pick up the foot and go again.
This really needs to be addressed and nipped in the bud ASAP. She’s learning something that could kill her or anyone who is behind her or heaven forbid, on her back once she’s grown. Because what’s she going to do if this never gets solved and someone puts a saddle on her? Or a leg over here? Or pulls on a bit in her mouth?
She’d be in a stall with her “helmet” on, attached to a blocker tie-ring every day for an increasing length of time were she mine. She might fuss a bit, but she should be safe and should learn to be patient.