For what I can add since I bought a new horse and my experiences with this matter:
When I visited the horse I bought before I bought her- she was much calmer and all. When she was brought to our barn we board her at-she was so nervous, skittish and even spooky- you nailed it- talk about a different horse! At first I was like wow, what did I get into? This horse suddenly had an issue with her back feet- wouldn't let me touch them without her kicking. Even having her belly curried she would fuss about. She danced on the cross ties, rushed when being led....
But what I did was worked slowly with her. Yes, I too didn't ride her right away- I wanted to develop some trust and bonding first. I'd put the horse on the cross ties in easy view of the other mare ( because now, my horse can't stand to be away from this mare friend she has) and I would talk nicely to her and groom her. It was rough in the beginning when I am used to an older lesson horse. But I would come in the evenings when it was quieter in the barn and work with her for short periods of time.
Then I'd start coming at other times. I would start to work with her feet, correct her when she would try to kick, lead her around, and just let her understand I wasn't hurting her, but working with her.
If she is really kicky, a carry a crop and hit her in the leg ( not hard, but enough that she knows something is coming and its not ok to kick) If she rushes when walking, I turn her in circles. I can calm her better on the cross ties and she doesn't have to see the other horse. She still can get a little any on the cross ties, but its never as bad as in the beginning.
So here we are 4 months later. Have all her quirky behaviors stopped? No, but they dramatically decreased. The whole buddy sour speil was a new one- but she eventually calms down in the ring when she is there and not the other mare. Sometimes she is just like the old lesson horse on the cross ties, sometimes she is a little ancy. I can pick out all her hoofs now, I learned what I was doing wrong and my horse is trusting me.
It can take time. Maddie, her buddy, adjusted a lot quicker than my horse did- but she is also 18 where mine is 8. I may not have the best advice due to not having years of experience, but my advice is to slowly work with your horse. Work to develop the trust and respect again. If you are nervous around her, she will be too ( my horse was!). Understand that the move has effected her, so help her adjust to the new barn by becoming her leader. You can start by just talking to her when she is in her stall/paddock. Do short sessions on the cross ties. Hand graze her. Lead her around the arena. ( bare in mind, i had help with my BO in the beginning, she would show me how to do things better and tell me what to do since I was used to an older lesson horse.)
As far as her arthritis, I don't have much advice with that, but as others said, make sure that issue is taken care of to eliminate that as a cause to her stress.
But good luck. I know its a bit discouraging, but work on slow and steady steps and be confident that you will regain her respect and trust.