Following the conclusion of Newhart, Duffy continued to work in television, playing the original Maggie Campbell on Baby Talk (1991) and Allison Sugarbaker on Designing Women (1991–1992).

[4] She appeared in supporting roles in the exploitation horror film Butcher, Baker, Nightmare Maker (1981), also known as Night Warning, as well as Cutter's Way (1981).

[5] In 1983, she played Princess Ariel Baaldorf in the medieval adventure spoof TV series Wizards and Warriors, which lasted one season on the CBS network.

In 1982, Duffy guest-starred on the sitcom Newhart as Stephanie Vanderkellen, a self-obsessed heiress and the haughty cousin of Stratford Inn maid Leslie.

[4] She continued to play Stephanie for the rest of the show's run, earning Emmy Award nominations for Outstanding Supporting Actress in a Comedy Series for the role every year from 1984 through 1990.

She appeared on The Suite Life of Zack & Cody as the rich mother of Jason, a boy who goes on a date with Maddie Fitzpatrick (Ashley Tisdale).

Most recently, Duffy appeared in a stage production of Guess Who's Coming to Dinner at the Huntington Theatre in Boston, directed by David Esbjornson, for which she received an IRNE Award nomination for Best Supporting Actress in a Drama,[12] followed by a lead in the play Sex and Education at the Laguna Playhouse in the spring of 2016.

[13] In December 2016, Duffy co-starred with Mare Winningham and Mark Blum in an Off-Broadway production of Rancho Viejo directed by Daniel Aukin Playwrights Horizons.

"[14] She starred in the ensemble comedy The Outsider at Paper Mill Playhouse in New Jersey, along with Broadway veterans Lenny Wolpe, Kelley Curran and Manoel Felciano, directed by David Esbjornson.

[citation needed] Duffy married actor Jerry Lacy, co-star of Dark Shadows and Love of Life, in 1984.