Amen!:yes:
All of our horses, come to think of it, have disliked the arena. One was a burnt-out schooling horse, another had a 5 minute attention span, an oldster hated being inside, and our present gelding feels pretty much the same way. We have worked all of them inside because that is where the vet takes them for lameness evaluations, colic walking, etc. I don’t want the horse behaving like a whackadoodle on the line as the vet is trying to get him to settle into trotting so he can see what is going on in the legs, feet, etc. So we get some of the arena-proofing done as we go along.
I also think it helps to have a place to work on the small details of riding, away from the distractions on the trail once in a while. You don’t need to burn a track into the ground along the rail, but refresher courses in small details or basic listening skills can pay off big dividends later out on the trail. Otherwise, I prefer being outside with my horse.
Edited to add: It always amazes me how horses who do lots and lots of circles in the arena all the time can stand it. I guess in that situation, you always know where you are and where you are going to go, so the boredom for some is security for others. If I were doing that all the time, I couldn’t stand it, so it makes sense some of them prefer the great outdoors. Just a thought.
Just one thing to think about, are you using the same tack when you do the arena work as you do when you go trail riding? Are YOU as relaxed? Just thinking of reasons why she would be so different.
Judy
Sounds familiar…my guy will do anything for me on the trail, however, in the ring, he looks as me like I have 2 heads! He also include a few bucks when I ask for a canter…but not on the trail…he’s in heaven!:lol:
Craig Cameron has some great episodes on RFD-TV on different things you can do in the arena. These exercises he suggests keep you & your horse from getting bored. They also help brush up on cues & communication. For example…one exercise he set up cones and showed different exercises to do just by moving the cones around…hard to explain…sorry. 
I am sure you can Google him and order videos off his website. I really like him…easy to understand and not arrogant. Just an idea…
UPDATE; Just a small update. I got to ride outside today (FINALLY!), it’s beautiful here, low 50s and sunny and NO WIND! Very rare for central IL. :lol:
She was amazing. We went bareback and with a sidepull, and this is our second ride after a 2 week break. She went along like we hadn’t missed a day, and every time we came to a fork in the driveway where she could either go back to the barn or go out further, she dove towards the path AWAY from the barn. Once we got back, she turned around and tried to head out again. She was like a little kid on a merry go round, she wanted just ONE MORE TIME! :lol: I couldn’t say no, so we did the little loop one more time. 
As for indoor riding, she’s slightly better. TBH as long as she doesn’t try and kill me in the indoor, that’s fine with me. She’s not horrible inside, but she makes it clear she’s not having fun. I live to ride outside, and so does she. It’s what makes us both happy, ultimately. 
