I suffer from osteoarthritis in my fingers and thumbs. My left thumb is particularly bad, and the top joint locks. Unfortunately, I'm left handed.
I have had strong NSAIDS which did help, but I could only have them for one month, due to the risk of gastric bleeding.
I had a hydrocortisone injection 💉 into the middle joint of my left thumb nearly three weeks ago. At first there was an improvement, but now it is very painful again. I have been told I may need surgery. My practitioner is ringing me in three weeks time to see if the injection worked. All very disappointing.
Sorry I couldn't be more positive. Hope your fiance has better luck finding a solution for her painful thumb. I have a thumb splint, but it gets in the way of everyday activities, and is awkward to get on and off. Sorry.

I also have pain nearly everywhere, but I have been getting injections in both thumbs for years. At first they helped for about 6 months, but now my left thumb has become so painful that I can't safely hold anything. I am having surgery this coming Thursday (10/13/2022) and although I am dreading it I have a wonderful orthopedist that I trust completely. He replaced my right hip last November and I went from horrible pain and being barely able to walk, to having no pain whatsoever. It's hard to believe the difference! I have absolutely no pain and can walk normally. I will write after the surgery and depending on how everything turns out, it might be an option for you.
Blessings and love, Beth

So sorry for your fiance.ad that's exactly what my right thumb and forefinger gives me locks it's living with it somehow..take care