Since this is revived and I am the OP, I just wanted to let everyone know that I have since moved my horse to a different barn (had a few lessons at new barn and my mare was so well behaved) and so my mare doesn't have any more spookiness issues, hence no need for a bit to help me 'stay in control' of a runaway mare - which is kinda what was going on - we weren't really doing much dressage at that point.
So new barn is awesome, my mare is now in a HS RS Dynamic eggbutt snaffle and might move to a loose ring version soon. We can actually canter at this new barn without it being scary and my mare is so calm and relaxed. A friend from the old barn came to watch us ride at the new one and she couldn't believe it was the same horse.
I guess my original question was a little less about dressage (even though I ended up showing in a snaffle and scoring 56 in IntroA at my first show - but had to switch back to the kimberwicke the next week - was still at old barn) and more about being safe on an unpredictably spooky horse who shouldn't be at age 20 with lots of eventing experience.
Either way, all is well now, thanks.