Where to start…First, stop the bit a month trials. Pick what has worked best for you so far and stick with it. As you’ve already learned, these Fjords are very smart and she has your number on that. If you are consistent and insistent, she will soon learn that that gig is up.
If she has been bolting and it worries you, ride in an arena for now. Be safe. You’ll both be happier. Your body will relax and so will hers. As calm an outward demeanor as these Fjords have, they can be internal worriers and pleasers that are very quick to read your tension. Your tension may be part of the reason she feels a need to bolt. I have two Fjords and one, although he is not at all a skidish horse, very much gets his confidence from his rider/handler.
Once you’ve helped your mare find her balance and lightness you’ll be able to get her out in the open again. All things in their due time. During the first year or so of owning our older Fjord, he would often buck going into the canter. It was never a nasty buck, just an “oh, *hit where am I supposed to put my feet so I don’t end up on my nose.” As my kids became more balanced riders and Mr. Fjord developed better balance, the buck disappeared and has never resurfaced. He’s quite opinionated and will let a rider know if he thinks he is not being treated well. In his early days, when work came harder for him, he’d even give a defiant grunt when he didn’t want to do what he was asked. If you grunted back at him, he’d give a head shake as if to say “fjcuk you”, but he would comply. He also has a great sense of humor.
I took over the ride on what had been my (now adult) kids’ Fjord 6 or 7 years ago after many years with my very soft mouthed TB. At first I really hated riding him because he was sooo heavy in my hands. And yes, he had one powerful neck that could pull you right out of the saddle if you didn’t have a very strong core. I’m 5’9" and have ridden for 35+ years, so no peanut of a rider. Still there were days.
I started out by going back to square one, pretending he was a green horse who knew nothing. We started with some ground work, but frankly we both enjoy ridden work more. He is very game and loves to work and please. His body is just built in a way that makes lightness more challenging than for some other breeds. He is very smart and actually quite nibble with his feet, so when he does get it right he gets LOTS of verbal praise and (his favorite) a little wither scratch.
Years ago someone told me “remember, it takes 2 to pull.” I still have to remind myself of that every now and then. I never used anything more than a French link egg butt snaffle on him. I also always carry a dressage whip. We started out doing a lot of just walk work - transitions: rein backs; halt from the seat only or a verbal cue but, no pressure on the bit; lots of series of ground poles, eventually raised 6 inches off the ground; circle of all sizes and spirals in and out; shoulder fore and shoulder-in; leg yield. All at the walk for maybe a month or more. Everything I did was aimed at 2 things: one, get him to shift his weight and energy to his hind end, and two to let him know that I would not allow him to support himself on my hands. He had to carry himself. That is non-negotiable.
Eventually we added rein back and then immediately forward into trot. If I had to, I’d use the whip to let him know that I expected a quick, light, and energetic movement forward. Just be careful not to catch him/her in the mouth when he/she responds or you will punishing him/her. It takes time to build the necessary strength, but once it’s there Fjords have plenty of it.
Keep your sessions short, varied, and as fun as possible. If he/she is getting tired I do one more thing he can do well (often that is just halt square) and then immediately call it a day.
As your mare becomes light at the walk, add in very short trot sets; short enough that she doesn’t have time to get heavy. This may initially be only a half dozen strides or so and then do a downward transition from your seat. Rinse and repeat all the walk work at the trot as she starts to get the idea of energy and lightness. Take whatever time and patience it takes. She WILL get it. Once you get to the canter, it will be pretty easy as she will understand what you want. But again time and patience will pay off.
I now love riding my Fjord and at 24 years old he still loves it too. His ears spring forward when he sees me bring his tack.
Good luck. Fjords are so fun! Feel free to PM if you have questions.