I'm not sure how you think I should go about getting her to accept the bit. She does give and listen, albeit certainly not as much as is ideal, and I can ride her in either a snaffle or a halter, though I get the best response with a curb. Actually, what she rides the absolute best in is a Myler ported Pelham:
She LOVES this bit. Which isn't to say that she doesn't still try to pull and fight on occasion, but she's very respectful and gives the most to it. So I save it for barrel racing so as not to desensitize her to its action. I use the Argentine snaffle on trails to try to keep her in a fairly mild bit so that she doesn't get even harder-mouthed and more bracey. I do have a long-shanked Myler with a different mouthpiece I could ride her in and that she also gives to, but I prefer to stick with the shorter shanks whenever possible.
Some issues are due to the rider, some are due to the horse's natural way of going and temperament, some are due to past training, some are due to ground conditions, some are due to equipment, some are due to "old habits die hard." She is braced and stiff even when being trotted by hand for veterinary evaluation, with ears pinned, neck stiff, and head high. I'll take the blame where necessary, but no more than my fair share.
I ride her as softly and quietly as I can. Is there room for improvement? Absofrigginlutely. I know I need to soften, and that's something I'm striving to accomplish. But it's not exactly an easy thing to do.
She's not trying to "run out" from under me. She's more than capable of bolting on a hell-bent course if she so chooses. She wants to go faster, and is frustrated that I won't let her, but despite her discontent she still chooses to listen and respond.
Even when I lean forward I do not push with my legs to encourage speed. My horse is accustomed enough to me (I'm the only person who has ridden her for years and years, and I was the one to break and train her) that she certainly knows what my body movements mean, and knows when I am and am not asking for speed.
When she braces, it is against herself and our combined tension in general, not against my hands at any point, in either video.
I do not *like* her way of going; I tolerate her way of going. While less than ideal for sure, it is apparently quite effective for her barrel racing. That is the only reason that I am not horribly concerned about it--she still works and wins. But I do wish to correct her for the simple reason that I want to minimize her chances of getting hurt again.