In season 1, it is thought that she is the daughter of the late William Walker and his mistress Holly Harper, Rebecca's mother.
Sarah (Rachel Griffiths), Tommy (Balthazar Getty) and Kevin (Matthew Rhys), the three Walker siblings involved in the family business, initially agreed to keep Rebecca's existence a secret from the rest of the Walker family, although Saul eventually told Nora about Rebecca.
Justin was the first Walker sibling to reach out to Rebecca, after meeting her and discovering that they had high school friends in common.
In another conversation, Rebecca told Justin that "there's a new black sheep in town, get used to it & I'm ready to move to a new city".
Nora (Sally Field) invited Rebecca to a family dinner, at which Kevin pulled out a strand of her hair to test her DNA.
Sarah, Tommy and Kevin extended social invitations to Rebecca, who agreed to meet them all at the Walker home.
However, she bonded with Sarah's husband, Joe (John Pyper-Ferguson), over a shared love of music, and accepted his offer of guitar lessons.
She also arranged a job for her friend Lena (Emily Rose) as the office manager at Walker Landing, the winery business that Holly operated in partnership with Tommy Walker, but this ultimately resulted in Lena sleeping with both Tommy and Justin.
However, things began to change when a former boyfriend of Holly's, a film director and photographer named David Caplan (Ken Olin), unexpectedly arrived for a visit.
After a series of events caused Rebecca to begin doubting what she knew about her paternity, she took a DNA test which revealed that David Caplan was her father, rather than William Walker.
She did not immediately tell the Walkers that she was not related to them, but kept the test results to herself until after Justin revealed that he had some romantic feelings for her.
The Walkers learned that the "R" in the computer password had never stood for Rebecca at all, but for Ryan (Luke Grimes), a child William had with yet another mistress.
In the final episode of the season, Justin and Rebecca acknowledged that they had feelings for each other, and began to discuss the possibility of commencing a relationship.
Later, Ryan Lafferty, the newly discovered half-brother for the Walkers gets a bit too close to Rebecca for Justin's comfort.
When their rehearsal dinner arrives, Rebecca and Justin have a huge argument that culminates in him telling her that he is unsure of everything.
A year has passed since the season 4 finale, and it is revealed Rebecca has moved out of the home she shared with Justin.
Justin also reveals to his family that while he was in Afghanistan they divorced, however, they still have feelings for each other, when Holly once again forgets that Rebecca is her daughter she turns to Justin for comfort, this leaves Rebecca confused about the future because she was offered her dream job of photography in New York.