In late 2004-early 2005 after moving into the house I am living in now, my cousin would spend the night like every other weekend. Well one morning my cousin woke up before me and went out into the computer room. I woke up probably an hour after her. I got out of bed and started getting ready for the day.
I was doing my hair and make up in my huge mirror and my mirror casts a reflection into my sister's room so you can see everything (the rooms are connected). Well after I finish with my make up I start putting gel in my hair. I look up and I look into the mirror and I see my sister get out of bed and walk out of the room. I continue to do my hair and when I finish I leave the room only to see that my sister is still sleeping. I clearly saw someone in a white night gown get out of her bed and leave the room, but she was still sleeping! I leave the room and I see my cousin.
My cousin says to me, "I just saw a ghost." I asked her what it looked like and she said, "It was a lady in a white night gown and it walked passed me when I was in the computer room." she saw the exact same ghost as me.
I haven't seen the ghost since but my sister has claimed to see it, or at least I believe it is the same ghost and others have claimed to see a fog or white cloud in the living room. I don't know if it's the same ghost but I find it interesting that most guests see something white. I don't know what or who it was, I haven't seen it since, however every now and then when I'm in the computer room (where my cousin was when she saw it) I get the feeling of being watched and I will turn around to find nothing.
I also was wondering if you had told your sister about it right off the bat, or did you wait until she mentioned something about it?