I’m curious about how bonding proceeded between the two of them. Depending on how large their space is, they may actually still be going through a territory pee/poop war, which would explain why both of them are having more accidents than usual. I don’t think there’s really a logical reason to believe rabbits can adopt other’s “bad habits”, so I’m trying to think what else may be coming into play.

EDIT: Ah, just revisited your bonding thread: https://binkybunny.com/forums/reply/1932677/   … it is possible that they are still sorting stuff out, even if there is no fighting.

Having weak hind legs means she is a rabbit who is special needs, especially if it is very easy for her to get her bottom wet and potentially get urine scalding. Owners with rabbits of special needs may need to adapt and create a more specialized environment in that case. Have you considered putting additional litter boxes around? I know you mention she doesn’t go in particular places, but it may be more tempting if there is simply a shorter distance to a litter box. I have 4 litter boxes around the free-roam area of my home for my rabbits. It’s not the most appealing, but it helped since one is not very good with peeing in the litterbox 100% of the time.

Beyond environmental changes, it is also good just to access if the increase in accidents may be caused by an underlying medical issue. Urinary tract infections, perhaps something with her hind legs may be influencing her control of her back end… have you consulted and had her assessed by a vet recently?