I've dealt with this a few times over the years. I've always just placed the additional box where it is needed temporarily (bedroom in your case) until kitty is used to her surroundings, it shouldn't really be more than a couple of days. Once everyone is acclimated to their new life I removed the extra box and showed the new addition where the permanent box is. I usually place the kitty in the box before it's cleaned so they get the scent of all of the wonderfulness. I've never had a problem. Just put the new kitty in the box a couple of times and she should catch on with no problem. Good luck and have fun with the new kitty.