In the book, Elizabeth was taken in by Victor's parents because her father married an Italian woman after her mother's death and thought it would be better to be raised by relatives rather than a stepmother.
In the film, Elizabeth was simply said to be an orphan.
Since childhood, Elizabeth and Victor were raised and lived as siblings in both the novel and film.
In the film, the relationship between Victor and Elizabeth was given a more intense and emotional twist: they were madly in love, going from "brother" and "sister" to husband and wife.