In addition to guest-starring roles on "Chicago Hope", "Boston Public", and "Third Watch", Duff became a familiar face starting in late 2002 as Amy Saunders/Sanders on the children's television series, "Lizzie McGuire", which her sister Hilary starred in as the title role.
Njen oče, Robert Erhard "Bob" Duff je solastnik verige trgovin za pohištvo skupaj s svojim očetom, Haylienim dedkom, Johnom B. Duffom, ki prebiva pri družini, saj želi voditi posle v Houstonu.