Smallville Season 10 Episode 3 (Smallville s10e03) with title “Supergirl” aired on Friday, October 8th 2010 at 08:00 pm via CW Network.
Here is summary for :

Clark is stunned when Kara returns to Earth and tells him Jor-El sent her to stop the dark force that is coming because he doesn’t believe Clark can handle it. Meanwhile, Lois confronts Gordon Godfrey, a shock jock radio DJ who has been crusading against heroes, after he threatens the Green Arrow. However, after Godfrey is possessed by the dark force, he takes Lois hostage and Clark and Kara have to come to her rescue.