The IMDB's Eclipse info has already updated to include Kirsten Prout has been cast as Lucy:

According to BD Horror News, "Kyle XY" actress Kirsten Prout will play the part of vampire Lucy.

Kyle XY alum Kirsten Prout has landed a minor role in the third installment of the Twilight Saga, Eclipse.Prout will play Lucy, the Southern vampire that that worked with Maria and Nettie before she was killed eventually by Jasper and Maria.

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