I have two cats. One of them uses the littler, and the other keeps peeing/pooping in the side of the couch. ?

They both have there each others littler box, it's in the laundry room by the dryer and washer. I don't know why she keeps doing it! My dad is going to make her an outside cat if she doesn't stop. We have tried lemon,vinegar,citrus smells, and even foil. Please of you have any advise please let me know. My dad keeps her in a bathroom by trawls with water,food, and the litter box for a night or two. Wen he's in there she does go to the bathroom in the box. But please please help. She is a calico cat. .