It could be emotions or stress. I left my cat for 18 weeks while I went out of province. Mother checked on her several times a day, but for the first month she didn't leave my bed. She didn't eat as much. She left the room to nibble, and use the pan, and get a drink. Cats can surprise you. I had a cat who would spend 13 hours in the room with me, didn't get food or water or use the pan, she stayed in my arms.
That being said, when a cat is sick, they will hide it to the end. Showing they are sick means they are vulnerable. It's a defense mechanism. Get her taken to a vet and checked out. She may just be on the loosing side of a territorial dispute, or it might be something much worse.