Chuck the twisted wonder bit forever and forget about headset for the time being. She is nowhere near ready for anything much past the bare basics of riding. I would start her over as if she had never been ridden and go back to groundwork. Get her bending and listening to you on the ground and work your way back up into the saddle. I can't say for certain, but I am willing to bet there is more going on in her mind than just being herd bound because for a supposedly well trained horse her age to suddenly develop such a serious issue as rearing (if it was sudden and she wasn't doing it before), there has been something wrong with the way she was handled before being turned out.
I really like your idea of going back to a regular snaffle and that's what this horse needs. Depending on her temperament and how long she's been turned out, you may not be able to expect her to just get right back into the swing of things. She'll need time to build up her stamina and her muscles again as if she had never been ridden.
Just start back at 1 and take your time. Work with her one day at a time and go at her pace, don't make a plan or a timeline because those never work. She'll progress as quickly as she is ready to progress and no more.
I won't say anything about side reins because I don't use them and never have.
Welcome to the forum
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I really like your idea of going back to a regular snaffle and that's what this horse needs. Depending on her temperament and how long she's been turned out, you may not be able to expect her to just get right back into the swing of things. She'll need time to build up her stamina and her muscles again as if she had never been ridden.
Just start back at 1 and take your time. Work with her one day at a time and go at her pace, don't make a plan or a timeline because those never work. She'll progress as quickly as she is ready to progress and no more.
I won't say anything about side reins because I don't use them and never have.
Welcome to the forum