Mate, that's awful. I'd def be getting some new curent x-rays taken, or even an ultrasound to try to get a more thorough look. To have signs of arthritis in only one joint in her body tells me she's hurt it/ injured it somewhere, somehow. Maybe unbeknowns to you?
I'm amazed they've (the vets) done nothing further to get to the bottom of it, TBH.
How long have you had her on alternative therapies each time you've tried something?
Have the vet/s even given her a course of injections, followed by further x-rays to see if any improvement has been gained?