Wow, this ended up being a much more interesting conversation than I had bargained for hahaha.
Well, thank you for all of the advice, I really appreciate it.
I understand and appreciate everyone's concern for my horse's arthritis, but the buck was simply a behavioral "spook" and I am 99% positive it had nothing to do with her being in pain. We had just finished a long ride and I was cooling her off at a slow walk, and I think it was the first week or second week that we had been at the stable, so if she had bucked me off it would have been earlier in the ride... not at the end, after she was warmed up and comfortable.
For now, I have decided to continue doing arena work and I've taken baby steps back onto the trail, actually in my dressage tack, by walking her halfway through one of the bridle paths (big step for me hahaha) and taking her into one of the paddocks to get her out of the arena. I'm hoping that when the spring comes, with nicer weather and better footing, hopefully my confidence will come around and we can do more on the trail and out of the arena.
Thank you for all of your opinions and thoughtful responses. Happy (almost) New Year!