Runyon is known for guest appearances or secondary characters in various sitcoms and dramas, as well as a couple of made-for-TV movies. Among her roles are Sally Frame on Another World (1981–1983), Gwendolyn Pierce on Charles in Charge (1984–1985), and replacing Susan Olsen as Cindy Brady in A Very Brady Christmas (1988). She starred in the horror film To All a Goodnight in 1980 and had a small part as a student in Ghostbusters (1984) alongside Bill Murray, and she starred in Up the Creek that same year.