The litter box habits may return, but they may not if the parasite has damaged her nervous system and kidneys too much.
There are some great tips for dealing with this on the disabled rabbits website (http://www.disabledrabbits.com/)
One thing I recently did for my senior who’s box habits had gotten worse was I lined his pen with washable pee pads and “sheepette” fabric, which is a medical grade faux sheepskin that’s easy to wash. This setup pulls the pee away so he stays dry and then I wash everything once a week. He does still use his box most of the time so more frequent washing might be necessary for you.
As for enrichment, I’m guessing things to chew and destroy will be popular with him. He may like phone books to shred, palm plates to chew, baskets, grass mats, etc.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.