This story was told to me by a friend of sister. It happened to her, but I am not going to put in their real names. Let's call the Mom Jane, and the daughters Susie and Jenny.
They're a regular family and have lived in their house for many years. The daughters grew up in the house. For years and years, the daughters would tell their mom about their friend who lived in the house named Sara. Well, Jane didn't think much about it.. believing it to be an imaginary friend. This went on for many years till one day they were getting ready to go shopping. Jane told the girls to clean their room first.. and being kids, of course they didn't. It came time to leave, and Jane saw that the room still wasn't clean. She threw a fit, yelling at them and threatening to ground them and insisted that as soon as they got home that room would be cleaned. When they came home, Jane took the girls to their room intending to point out what needed to be done. The room was spotless! Jane couldn't figure it out, even when the girls kept insisting that Sara must have cleaned it. This is when Jane started to become a believer. I guess at this time Sara started to become a little braver. Sara would play ball with the dogs in the hall. No one saw her, but the ball would bounce down the hall all by itself, and the dog would fetch it and take it down the hall and lay it on the floor, then look up wagging his tail. The girls got older and talked about Sara less and less. One day, Jane was sitting in the family room when she caught a glimpse of something in the dining room. She looked over and there stood a girl in an old fashioned night gown. Jane asked her, " What do you want?" and Sara replied, " I want my mother". They never actually saw Sara again, and when the girls grew up and moved out, there was never another sign that she was there.