Rebecca Crane

Rebecca Crane is one of the modern day Assassins introduced in Assassin's Creed II. She is the creator of the Animus 2.0 - which she affectionately refers to as "Baby" - and provides technical support for the Assassins alongside her partner, Shaun Hastings. She appears to be an old friend of Lucy Stillman, although, prior to the game, the two purportedly did not see one another for seven years, perhaps due to Lucy's internment at Abstergo.

In Assassin's Creed II, Rebecca serves as tech support for the Animus 2.0. She often leaves notes within the database entries that Shaun makes available for Desmond Miles while he is in the Animus, especially if the entries (i.e. about a particular structure) indicate the presence of a glyph or Assassin's tomb therein. The data module that Rebecca receives from Lucy with the records of the Abstergo version of the Animus allow Desmond to interact with the encrypted file Subject 16 left behind in Ezio Auditore da Firenze's memories.

Biography
It is unknown whether Rebecca is a 'proper' Assassin like Desmond and Lucy are; she makes allusions, but nothing is ever said conclusively about the nature of her place in relation to the Assassins. She did, however, play an important role in inducting Shaun Hastings into the Order. When Shaun, with his gifts for connection and conspiracy, endangered his own life by trying to tell the world what Abstergo was up to, Rebecca saved him from Templar silencers, and recruited him as an Assassin.

Assassin's Creed II
In Assassin's Creed II, Rebecca monitors the Animus to make sure nothing goes wrong (such as what happened at the start of the original game). She often provides small comments with Shaun's Landmark Database entries, particularly when the building either has a Glyph or a secret entrance to an Assassin's Tomb. More often, though, she will provide a comment relating to being at the top of the (usually quite tall) building, such as remarking that "the view must be great" from the top of a church or that she thinks Desmond is itching to get to the top of a bell tower.

Aside from providing technical support for the Animus and her small segments of banter with Shaun and Desmond, Rebecca doesn't play a significant story role until the end of the game, when she helps Shaun pack up the Animus gear while Desmond and Lucy defend their location from Abstergo. As they escape into a truck, she is able to get the Animus working inside it, which allows Desmond to re-enter the Renaissance and finish any remaining memories while on the way to their second base up North. This consequently allows the player to finish up any Side Missions and plot elements they may have missed, such as Races, Assassin's Tombs and Feather collecting, to name a few.

Characteristics and Personality
Rebecca is an energetic, somewhat immature young woman - despite the fact that she saved his life, Shaun Hastings is quick to belittle and gibe at her. She is tolerant and and optimistic, representing Shaun's foil - she is the polar opposite of her colleague, friendly and talkative, and seems quite sure of herself seems to talk and act in a rather "street" type of way - she may be conceived as being a little tomboyish. It has been speculated that she may have some relation to Rosa, since the two bear a striking physical resemblance. She shows great pride in her work, praising her redesign of the Animus as having a far more enlightened and creative construct; a "competitive edge" as she calls it. She also remains convinced that, despite Shaun's dubiousness of their means, the Assassins are, as Desmond puts it, "the good guys".

Trivia

 * When in the Animus, Rebecca adds information to the Database using the name "REBECCAC84". This may mean that she was born in 1984, making her 28 as of 2012.
 * Rebecca's looks are reminiscent of the Renaissance character Rosa, specifically the scruffy, dark hair. Another comparison between the two characters is that, when Ezio is mastering a new climbing ability, Rosa challenges him to race to the top of a building and back under time pressure. In a comment for a different building in the same area, the Santo Stefano, Rebecca comments that she would like to race Desmond to the top of the building if she were there.
 * When Lucy and Desmond first enter the hideout, Rebecca greets Lucy and exclaims : It's been so long. Seven years!. This could mean that the last time the two friends saw each other was in 2005.