From Wikipedia, the free encyclopedia. Aisling O'Sullivan (born 1968 in Tralee, County Kerry) is an award-winning Irish actress who starred in the movie The Butcher Boy as Francie's mentally unstable mother. O'Sullivan previously appeared briefly in another Neil Jordan film, Michael Collins. She had a part as the grieving mother who commits suicide in Six Shooter, playwright Martin McDonagh's Oscar-winning short film. She is familiar to Irish television audiences as Dr. Cathy Costello from Series 1 to Series 5 in the hugely popular drama ser…