Advice Needed for Co-worker, Bunny is 5 yrs old, I gave them a 3 month old kitten in Dec. Bunny not happy

Hi all-

In Dec. a person I know trapped a 3 month old kitten, my co-worker adopted the kitten. She is a good girl, no problems at all. She doesn't mind the bunny, sometimes she will chase the bunny but sometimes the bunny chances the rabbit. The bunny is a boy and he is 5 years old (he's neutered as well), during the 5 years he has lived with their black lab and never had any issues. He would occasionally leave a poop behind but it wasn't a lot. Now since Lucy the kitten showed up, he is urinating inappropriately, pooping all over the place. Lucy isn't one that likes to be held so she just does her own thing and at first she got a lot of attention but now they are trying to make sure the bunny gets enough attention but Saturday night he pooped all over the living room a lot. My co-worker is at her wits end. He is constantly peeing on the carpet outside the bathroom door which is where his cage is and litter box is, his litter box is clean. Any suggestions?

Bunny is obviously unhappy, and expressing himself the only way he knows how. He sees her as a threat, and is marking his territory accordingly. How did they introduce them? Did they do it gradually, like one would with two cats, or just bring her home and expect things to be fine? Is the kitten allowed everywhere? If she has been around his litterbox, he could not want to use it, and if it where she can see it and get to him, he knows he is vulnerable when using it.