She and friend Kathy Najimy wrote and starred in two Off-Broadway shows, The Kathy and Mo Show: Parallel Lives (1989) and The Kathy and Mo Show: The Dark Side, both of which won Obie Awards.
Gaffney appeared on the British television talk show The Full Wax starring Ruby Wax, in which she portrayed American correspondent "Taffy Turner", in the recurring segment "Taffy Turner: Inside America". Gaffney teamed up with Jennifer Saunders in a recurring role as Bo in the sitcom Absolutely Fabulous; in 2004, talks of a spin-off show began but nothing surfaced. She is co-host of the "Women Aloud" radio program on Greenstone Media.
