My cat, all-of-a-sudden, is going to the bathroom in the house. We live in a two-family home with my mother and her cat living upstairs. Her cat, on occasion, got into our basement (which is where my cat boxes are). Over the years, this has not been a problem until the other night. My mothers cat got into our basement and terrorized my two cats. Ever since, my cat Isabelle has been using the bathroom in a bedroom, kitchen, and bath. I understand she was afraid to go back into the basement. I cleaned the cat boxes out and all around them. And then I locked her down there for the day to show her the "other" cat wasn't there any more. Well, that didn't work... she still went to the bathroom in my home. Isabelle is about 4 years old and this has happened over only 3 days. It seems like this is how it is going to be from now on. I don't know what to do. If this doesn't stop, I will get rid of her.
Your Isabelle is definitely traumatized. It is completely normal and natural that your cat is afraid to spend any time in the basement using her litter box after she was so traumatized, but there are a few things I can recommend to potentially help the situation.
First and foremost, try to find a way that your mother's cat never has access to your cats' space in the basement. I don't know how the living arrangement is, but if possible, keep your mother's cat away from your cats at all times.
Secondly, one day in the basement may not have been enough to help Isabelle with her fear. If the basement is finished, warm, and comfortable enough for her, you might need to keep her down there for 3 or 4 days. If doing so seems too stressful for your cat, you could meet with your veterinarian to discuss using a mild tranquilizer to help relax her.
Additionally, you should consider adding litter boxes upstairs in the main living areas where Isabelle is currently relieving herself. If kept meticulously clean and away from your mother's cat, these additional litter boxes may be a temporary arrangement for Isabelle. She will have somewhere safe to relieve herself while she is so stressed and traumatized, and she may gradually return to using the box downstairs in the basement. However, if she doesn't return to using the basement, the litter boxes in the main living area of your home could hold to key to keeping your precious Isabelle.
To read more about litter box problems, please click here. Also, you will find many similar questions and answers with more suggestions on how to handle litter box problems and traumatized cats.