I saw my sister recently.
Where did you see her? Where was she?
I saw her in my room.
It is good to have relationships with your siblings. If you don't want them in your room you should tell them nicely.
I didn't tell her to go away. But, I don't like her being in my room.
It's perfectly reasonable to want to have your room to yourself. Let your sister know that you aren't comfortable with her coming in univited.