Oh, I’m sorry, that must be sad to see. Rabbits though are amazingly resilient (it can affect us more emotionally then it affects them)…. and she has your love and affection to keep her spirits up. However, physically, she may need pain meds and if she does have arthritis, there may be some things you can do as well to help — like glucosamine. That helped Jack’s arthritis — his was mild though in his spine. (worse in his front foot).
I would call your vet and let her know what’s going on so you can start working on what may keep your bunny physically comfortable if doing binkies or other bunny acrobatics seems to cause her to fall.
Have you noticed that her legs or the way she hops in general is different?
Another thing to keep in mind is the possibility of e.cuniculi as that can cause hind leg weakess in some rabbits as the nerves from the brain to the hind legs can sometimes get messed up and cause a bit of an imbalance at times. My bunny Bailey was afflicted in that way, (she had spine issues and e.cuniculi, but with diffferent treatments she improved. However, the way she hopped was not the norm— with her, it’s not like she would be hopping normally and then suddenly fall over. She always had sort of a goofy hop (her legs would not stretch out as far out in her gate — they would always tuck in more tightly than normal bunnies). Again, this is not to scare you, as Bailey was a happy active bunny, but it is something to bring up and discuss with your vet.