Edelstein recently signed up to appear in several episodes of the show as a lawyer defending a doctor against allegations of malpractice.
Edelstein has now told TV Guide that her character Celeste is a good foil for Alicia (Julianna Margulies).
"Celeste has more pliable ethics and she's free in a way that Alicia can't be," she said. "It makes for nice opposition."
Edelstein added that Celeste "shares some colourful history" with Will (Josh Charles), explaining: "We partied around a bit."
Edelstein has previously suggested that she would like to continue working on The Good Wife and the show's executive producer Robert King has admitted that he would like her to stay.
Dylan Baker recently signed up to return to the show, while the list of other stars who will make appearances in the new season includes Parker Posey, Michael Arden, Harvey Fierstein and Bill Heck.
The Good Wife returns with its third season on September 25 on CBS.
> 'The Good Wife': See the season three poster
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Watch a trailer for the third season of The Good Wife below: