Who is Alice Cullen from New Moon and what is their importance?

Alice Cullen is Edward's adoptive sister. She is small, petite, and pixie-like, with short, cropped black hair. She is probably the most graceful of the group, as the way she walks would "make even a ballerina jealous." She's usually very cheerful and is surprisingly friendly towards Bella before Bella's been properly introduced to the rest of the Cullens. Alice has the gift of foresight; however, she only sees the outcome of people's decisions, not the motive behind them. Because of this, her visions change frequently if the person she's watching changes their mind.