Kerr was born in Cincinnati, Ohio. She attended the Cincinnati School for the Creative and Performing Arts. She also apprenticed in the Cincinnati Ballet Company. Before acting, Kerr was a singer and dancer on cruise ships.
In addition to Buffy the Vampire Slayer, Kerr is best known for her role as Nurse Ruth Ann Heisel on Desperate Housewives. Other notable TV credits include recurring roles on Pretty Little Liars, E.R., Six Feet Under, Reba, George Lopez, Bernie Mac, and The District.
Dagney has appeared onstage at Geffen Playhouse and Ford Theater, as well as mounted one-woman shows at The Hudson Theater, such as her original musical-variety show Holiday Fever!. Dagney has also appeared in commercials, for brands including Walmart, Miracle Gro, Allstate, Purina, Land o' Lakes, Ace Hardware, Audi, Alive!, Zaxby's, and Activia.