No worries. I just thought I should answer in case this is a spinal issue for Boo, or if she hasn't been the most mobile bunny I suppose it could be muscle wastage as it can be the same for us as we age. I don't think, despite having exercise pens, that Fiver ever really moved enough to keep himself fit, plus he had a bad start in life being the plaything for 4 rambunctious boys aged about 8 years old. He was returned to Petco and adopted out again to a place where he was kept in a dark basement pen and returned again. Then we found him.
Perhaps Boo is just aging, but it wouldn't hurt to ask your vet about it if it's really troubling you. I kind of wish I'd bugged my vet about Fiver more instead of just chalking it up to arthritis and thinking metacam would keep things level. But it's still sad to see our companions get older and frail. ((((((Huge hugs)))))) xxxxx