Every time my sister comes to vist she ruins my stuff

Every time my sister comes to visit with her kids they use my room because we live in a  relatively small 3 bedroom house. My mom and her boyfriend in one room. My grandma in the other and mine. Every time my sister comes to visit with her 3 kids they stay in my room. And something of mine always seems to be ruined when they leave weather it be my bed or dresser with stains from popsicles, dirty diapers left in my room. Food around my room. And I’m kinda weird with germs. I don’t like to sleep on anywhere other people have. I can’t stand knowing germs are around me if I think about it for too long. I don’t like sleeping anywhere but, my room because that’s the only place I know what’s dirty and what’s clean. I usually end up having to sleep on the couch when she’s here which I don’t like because I feel it’s not sanitary. I will  literally stay up all night when she’s here because I can’t sleep on the couch without feeling dirty. When I try to voice  those concerns to my mother she dismisses them because my room is dirty sometimes so obviously I don’t mind germs but, the only germs I’m okay with is my own which sounds kinda weird but, she’s coming again tomorrow and I don’t want her to have my room because I don’t like to go through cleaning my bed and everything when she leaves plus me not sleeping and everything. What should I do?