I see you mentioned elsewhere that automatic boxes probably won't be sufficient. While I generally wouldn't recommend a litter box that fully disposes of the waste automatically (because scooping the poop might be the first or only warning sign of health issues), something like the Cat Genie might help.
If Kika is willing to use an enclosed litter box, you might create a litter box enclosure using one of those pet doors that can be set to unlock only for specific animals based on their microchip or a collar tag.