my adult cat stopped using litter box

Question
I have an adult cat approx. 5 years old. She has been litter box trained the entire time. I recently brought a new kitten home about 4 months ago. she is an indoor/outdoor cat and I do not see her using litterbox each time, however, about two days ago i found the first of four poops so far in one of my rooms. She is usually really good about using her litter box or scratching at the door to go outside. I am shocked and have no creative way to retrain or help her. She tolerates the new cat but does not socialize. She, to some degree, does seem irritated and not comfortable the last few months. I suppose it may be stress related, but still have no clue how to manage or help the situation. I cannot allow for her to do this. Please help

Answer
Hi Kimberly,

Unfortunately cats have no other way to express their displeasure with a situation than to do this sort of thing.  Are you giving the older kitty as much attention as you used to?  She probably feels jealous and a little miffed that this pipsqueak has entered her territory.  Try giving her more attention and playing with her and the kitten together.  You can also get something like "Rescue Remedy" (get it at your local pet store) to put in the water to help calm her down.  There are also plug in pheromone emitters, such as "Comfort Zone" that do the same thing.  
Clean the area well with a cleaner that uses enzymes, "Nature's Miracle" is one but there are a lot of similar ones, to completely get rid of any smell and close her out of that room if you can until she gets under control.
You didn't say if the feces look normal or not.  If she is having diarrhea then she might be trying to tell you something and you should get her to a vet, but I assume this is a behavioral issue and using what I've told you it should resolve itself.  Just be sure to give her LOTS of attention and praise her if you see her using her box but don't make a big deal of it if you find the poop again.  If the only attention she's getting is negative attention she's going to keep on doing what she's doing.