She often disagreed with McCoy over their trial strategies in cases where she sees the defendant's crime as a byproduct of social circumstances, such as homelessness or racism. She had an especially troubled relationship with Branch, a conservative who replaces Lewin as District Attorney in 2002.
In the 2002 episode "DR 1-102", Southerlyn is brought before the New York Supreme Court, Appellate Division's Disciplinary Committee after promising to get legal help for a murder suspect who had taken hostages, to get him to release his prisoners. The man had a knife to a woman's throat and demanded a lawyer. Southerlyn, who happened to be in the area, volunteered to enter the store where the holdup was taking place, to negotiate the hostage's release. Since the man had asked for a lawyer, the committee attempts to paint Southerlyn's actions as fraudulent, since she was supposedly representing herself as his lawyer (which she denies), when she was in fact a district attorney. McCoy, who had been brought before the committee himself in the 1998 episode "Monster", represents her. She is reprimanded, but keeps her law license.
In several episodes, Southerlyn is portrayed as opposing the death penalty, which often puts her in a difficult ethical position when working with McCoy and Branch, who both support capital punishment.
Röhm left the show in the middle of the fifteenth season, and made her last appearance in the episode "Ain't No Love." She was replaced by Alexandra Borgia (Annie Parisse).
Her departure was noteworthy due to a surprising conversation between Southerlyn and Branch in the very last scene of the episode. At the close of the show, Branch dismisses Southerlyn because he feels she is too sympathetic toward defendants, and that her emotions get in the way of looking at the facts. A stunned Southerlyn pauses for a moment, then asks, "Is this because I'm a lesbian?" Taken aback by the accusation, Branch protests, "No. Of course not. No." Her final line is "Good.... Good."  This is the first and only instance that Southerlyn's homosexuality was ever explicitly mentioned, although there had been subtle hints in earlier episodes. In the 2004 episode "Gov Love," she is uncomfortable with a case in which McCoy successfully seeks to have same-sex marriage declared illegal in New York in order to get testimony from a gay defendant's spouse. Southerlyn had objected to this and refused to assist McCoy, but her sexual orientation was never mentioned.
She mentions in another episode that she dated a male college student while she was still in high school and that he is now a New York State Senator.
Series creator Dick Wolf later explained at the Television Critics Association press tour that he had consulted Röhm before scripting the scene — the only Wolf-authored scene in the installment — saying, "Do you want to go out with a bang or a whimper?" He characterized the scene as "unabashedly a water-cooler moment. And the fact that we're discussing it shows that I think it worked as a water-cooler moment." Wolf also noted the effectiveness of the device by reporting that the show's main online chat room "crashed 15 minutes after the show was over," although critic Alan Pergament joked in his column that the response came not because viewers approved, but "because many fans thought the out-of-left field ending was a crime."
TV Guide called Rohm "arguably the most inept cast member" in the series' first 18 years, with Ben Katner writing "we are dancing in the streets" upon her departure. Dusin Rowles of Pajiba described Rohm as a "disaster" and a "catastrophe".Entertainment Weekly called Rohm's performance and character "wooden".AfterEllen.com reported that Southerlyn was "one of the show's more disliked characters" due to her "cold and robotic" portrayal.
^ abKate Aurthur and Lawrence Van Gelder. "Battling crime shows" (TV ratings column), The New York Times, January 15, 2005, Section: The Arts, page 8: "Wednesday's episode featured the departure of Elisabeth Rohm ... as an assistant district attorney. 'Is this because I'm a lesbian?' she asked as she was being fired, much to the surprise of viewers, who have been shown little about the characters' personal lives."
^"Ain't No Love". Law & Order. Season 15. Episode 13. January 12, 2005. NBC.