Why does my roommates cat continuously enter my room?

[FantomElite]

Every night before I go to bed I slightly close my door. My roommate however leaves their door wide open. After awhile their cat keeps trying to enter. Mainly because I want to keep her away from my own cats litter box which she's used on before and pee'd on the sides causing a mess. I've done many things to tell her she's not allowed in with spraying mist her direction. Pushing her out the door, etc. Nothing that won't hurt her because I know what is too cruel of an act to do to a pet. why does this continue?