It's a movie where a mother adopts a girl and her biological daughter is jealous of the girl and in the end she tries to push the adopted girl off a cliff and she too almost fall off the cliff and the mother comes and the mother comes and grab both of them hands but she can only save one of them and she chose the adopted daughter.

Are you sure it was girls? It sounds more like this film... The Good Son (1993) - IMDb (http://www.imdb.com/title/tt0107034)

I´m pretty sure it was with Macaulay Culkin and the woman had to choose between her nephew and son.