A former figure skater, she competed in the 1988 U.S. Championships in junior ice dancing with her skating partner David Schilling, and finished in 13th place. When a stress fracture ended her skating career at the age of fourteen, she decided to try acting. She is best known for her role as Darla in Buffy the Vampire Slayer and Angel. She also portrayed Rita Morgan on Dexter 4 seasons, for which she won the 2006 Satellite Award for Best Supporting Actress and the 2009 Saturn Award for Best Supporting Actress.
Benz next took a recurring role on Desperate Housewives as Robin Gallagher, a stripper with a heart of gold and a master's degree in education who gets offered the chance to transition into a more legitimate career. The character of Robin is further developed when the audience discovers she is a lesbian and begins an affair with housewife Katherine Mayfair (Dana Delany). After the season-four finale of Dexter, Benz returned for the season-five premiere.
In 2013-2015 played the main role of
Amanda Rosewater in the Defiance.
Her film roles include Jawbreaker (1999), The Brothers (2001), Rambo, Saw V and Punisher: War Zone (2008), The Boondock Saints II: All Saints Day (2009), and Bedrooms (2010).