I know she is getting bored
I can't trail ride her because she spooks and takes off and my mom wont let me jump her until I can do my 1st level test with her. For a normal horse the stuff I do with her should not be boring, we only circle a lot when she is being bad other that that we do some upper level dressage movements with her so she doesnt become bored. I want her to have fun and i want to have fun but I want to get somewhere with this horse as she has a lot of potential.
But make it more fun to ride. Upper level dressage movements are hard and require a lot of focus and if she's sore (which she may be as Duffy touched on) it will do more harm than good.
When I ride my horse, gather we don't canter under saddle as I haven't learned how yet, we start off warming up on the rail.. twice each way (it changes every ride) on a nice loose rein, then we move to figure eights and I start asking him to march and start gathering up my rein. Then we walk a few circles in the corners and in the middle of the arena. Then I pick up the trot on the rail first (he has trouble staying on the rail) then we move into figure eights, then we work on serpentines, then we go back to on the rail, then we go over a series of poles I've set up in the arena. Then he gets a quick walk break on a looser rein (working on the free walk haha) and then I pick up a sitting trot and we work on leg yields on and off the rail. Etc. Etc. etc. He never gives me trouble, he's keen to follow orders, and he's never refused to do something. It's always "would you like some cream with your coffee?" instead of throwing a cup of black coffee at me.
I think mixing it up would help. Or just doing a short ride with a few circles and figure eights then hopping off and doing a bit of groundwork with her before letting her eat grass or giving her a handwalk through a trail.
It'd help :)
Chiropractor is not expensive & solves a myriad of problems & rules out others.
1st Video- I know its difficult, but when she kicks out, you pull back on her mouth- hard. It is hard, and its easy for me to say it BUT MOVE HER FORWARDS. She is a baby, I understand that, but in both video's she's working more with her front than her hind.
2nd Video: You said she's got mild navicular? All I'm going to say is I hope you're not planning on jumping her. It may be my imagination, but she looks slightly short on the front. You need to get her working from behind. I watched the video with the sound off, so I don't know what your trainer is saying. GP dressage rider or not, she's not a vet- I would serisouly get her back checked out, that's not naughtiness in my eyes, that's OW MUM, THIS HURTS. Get it checked, and then see if there is a difference. And the saddle checked too. Heck, mine competed GP and bred her own horses, but she'll give my saddle a look but she would never say this fits 100%- that's why we pay saddlers. Also- not criting riding here, I promise ;D But try and keep your inside leg on her more and hands stiller, inside hand drives her forward with impulsion but yours fishes whilst your outside leg is relatively still.
All in all she's a nice mare, but if she has navicular, like my dad's horse, if its on the front you REALLY have to ride them properly from behind otherwise they'll get foot sore. Not so much lame, but that little limp.
Good luck, the more engaged her mind and forward her body, the better ride for you both and you will be able to turn that potential into something more.
Have fun with her :)