She also recalled filming the 2008 drama Easy Virtue alongside Colin Firth and Kristin Scott Thomas, before returning home at weekends.
“I remember being in Ponty in the opticians and people were saying ‘are you filming with that Colin Firth?’ and I was like ‘sort of yeah’,” she told Lewis in January.
“But mainly, nobody cared,” she said, adding: “I never get recognised in Ponty hardly ever.”
Any conversation she does have about her work are matter-of-fact and brief, she said.
“I think what helped me stay who I am is that I have lived in Pontypridd the entire time.”
In the Sky crime series, Nixon plays Shell Hill, the mother of a nine-year-old girl whose death shocks the fictional town of Morfa Halen.
It marks another major role for the Welsh performer, who has built a career across film and television, including in comedy Fresh Meat, about life at university, and the four-part drama The Guest.