I am strictly a trail rider. My "training" goes back to my grandad who raised Welsh/Morgans.
While the driving bit was different, back in The Old Days, all that was available to us was a short-shanked curb bit.
Regardless of whether I was trail riding a trotting horse or a gaited horse, I have always used a low port curb with swivel shanks (once I learned about swivel shanks), because low port bits are what I am used to.
Unless the horse just was not happy with a bit in its mouth, of which I have wasted a lot of money buying a gazillion different types of "recommended" bits.
Then I use a mechanical hackamore. My 27 yr old Arab and my 19 yr old TWH have both worn mechanical hackamores their entire lives; both Sellers told me that's what they used.
I tried those "recommended" bits on both horses and they were having none of it, so I've stuck with the hackamores.
The Arab was a lesson horse for children under 12 for several years and nobody ripped his head off with the hackamore.
My TWH is full of snotty attitude but he has never, in 16-1/2 years tried to run away in the hackamore. When we were doing a lot of riding, I rarely used the reins. I ride without saddle and he was just as happy with seat/leg cues. Make sure your horse doesn't have a thick tongue or a low palette before you start experimenting with bits. If she happens to have either, that alone, will send you in search of an altogether different bit than what many of us might recommend
As far as head set? I trail ride - I let the horse set his head where it was born to be comfortable. Where they like their head when I ride them, is pretty much where that head is when they're gaiting at liberty in the pasture.
Unless I had the horse in my avatar in a parade - then I would tell the show off "git that head up Duke, people are looking at your handsome self" :)
My recommendation is whatever makes her happy and she listens