Bonnie Somerville has been cast in as Christa, Harden's former role, reported Entertainment Weekly.
"Code Black" is a medical drama set in the busiest and most notorious emergency rooms in the nation, where the extraordinary staff struggle in the face of a broken system to protect their ideals and the patients who need them the most.
Harden will now play Leanne, the residency director in the ER.
Christa (Somerville) is a former soccer mom whose son died of cancer, Christa is now a newly minted, talented and dedicated doctor whose experience handling her son's disease, coupled with her intuition and life experience, makes her see things that often escape her younger fellow residents.