The White Lady

"I was home alone for a weekend a few years ago while I was still in high school. After school one day / was driving home, and when I passed in front of my house / thought I saw some old lady in white clothes in my sister's room looking through the window. / thought it was stupid, so I went in the room to check out what it actually was, but I couldn't find anything. I pretty much forgot about it until later that night / got a call from a very panicked and scared neighbor saying there was some old lady pacing back and forth in my sister's room. I still have no idea what it was, and I've never seen anything like it since. "