Who is Rosalie Cullen from Eclipse and what is their importance?

Rosalie Cullen is another of Edward's vampire sisters. Rosalie has never really liked Bella and was an active voice of dissention when the family had to make the choice whether or not to accept Bella into their family. However, now that Bella has made the choice to become a vampire, Rosalie seeks her out to give her reasons why she should not make such a choice. None of the Cullens became vampires willingly and do not know anyone who has. For this reason, Rosalie shares her story of how she became a vampire in the hopes of convincing Bella that she already has everything she could possibly want and should not rush into becoming a vampire in order to be with Edward.