A male relative or friend threw her off the cliff. At one scene this little boy is locked in the closet and he can't get out, later he finds a piece of hair on the floor. Later or before he has a vision (seems as if it is happening at the moment) of the little girl in the closet and being dragged out by someone.

Lady in White (1988) (http://www.imdb.com/title/tt0095484/)

Great movie.. Lucas Haas was very young in this movie. I found a copy on Ebay a couple of years ago.