Arena sour horses can be a real problem. She is 12 years old and has never developed a good 'work ethic' and has a less the 'willing' attitude. Some of these horses never make good arena horses. But then, part of it may be the way someone has ridden her there.
This is what I would suggest. I would develop her work ethic on the trail. I would do a LOT of jogging/trotting on the trail and would find and identify every place where you can jog or lope a circle. I would lope several hundred yards at a time on the trail in her least favored lead. This will, at the least, get her comfortable in both leads.
After only a few 'working' sessions on the trail, you will find out if she is just resistant in the arena or if it is the 'work' itself she is resistant to.
Then, when you get home, go out to your 'arena' spot, jog a single circle, get off, loosen your girth and lead her back to the barn.
When I do this with a roping horse that is bad in the box, I always end each riding session in the roping box, dismount there, loosen the girth, take off the bridle and lead him out with tie-down.
I have done this many times with arena sour barrel or roping horses -- some that three people could not get into the arena.
To keep show horses (like a reining horse) from getting arena sour and wanting to leave the arena, I would always take a reining horse, after working a class, out to a training area and ride the horse harder there than I did in the ring. Then, I would get off, loosen the girth, stand around a while and finally take him back to the barn. If you want a horse to get stupid about being in the arena, just work him there, ride him out, go straight to the barn and let him rest there.
When people ride here, either for lessons or as I have an apprentice right now, one of the first things they learn is that I never want them to ride a horse out of the arena or in from the pasture if they are riding there. I want them to stop out where they were riding, make the horse stand perfectly still for a few minutes, then dismount, loosen the girth and lead it back to the tack-room. Some horses are then girthed back up and ridden off again if they get too anxious to get back to the barn. I try really hard to stop bad behavior before it starts.