According to TVGuide's Ausiello:
"Samaire Armstrong, who plays Juliet, brat-astic celebutante and fraternal twin to Jeremy, will not be returning to the series full-time, sources confirm to me exclusively. A spokesperson for ABC Studios declined to comment, but a Dirty Sexy insider tells me that producers decided not to pick up Armstrong's contract option. The actress is, however, expected to appear on a recurring basis, her schedule permitting."
Read more about it HERE.