Shaffer was born in Woodbridge, Connecticut, where she showed an interest in acting early on in her life. After finishing high school, she attended Connecticut College for Women, then Yale Drama School. Shaffer is a coloratura soprano was trained at Juilliard.
Throughout her life, Shaffer has appeared in numerous soap operas, including Hidden Faces, Search for Tomorrow where she played two separate roles; that of Emily Rogers Hunter and Stephanie Wilkins, Where the Heart Is (in which she played James Mitchell's stony and somewhat snobby sister, Allison Hathaway Archer Jessup), The Edge of Night (where she played Serena Faraday/Josie), All My Children, and Guiding Light. However, her most recognized role was that of Rae Woodard on Ryan's Hope, a role she played from 1977 to 1984, and then reprised for the show's finale in 1989.
She was nominated for two Daytime Emmy Awards for her portrayal of Rae Woodard on Ryan's Hope; she won the award in 1983. In addition to her daytime roles, Shaffer also had a role on the short-lived Norman Lear sitcom All That Glitters.
As Shaffer aged, it became increasingly obvious to her that it was getting harder to find steady work as an actress. Partially because of this, she began writing for soaps instead of acting on them. Since the late eighties, she has written for Ryan's Hope, Loving, General Hospital, and As the World Turns.
In addition to scriptwriting, Shaffer has written numerous books.