How to stop a cat from going to the bathroom out of her box.

So my cat that will be a year old in July will go to the bathroom out of her kitty litter box and go to the bathroom downstairs by the door to get into the basement. I can't really move the box because it's a tight space. We just got another baby kitten 2 weeks ago but my other cat has been doing this for a few months now so I know it's not because she's jealous or whatever. How do I make her stop? Could I spray something down ? She was really good about using her box then one day she felt the need not to. 😒😒