Since her creation in 1959, Supergirl has been killed, temporarily replaced with non-Kryptonian versions and rebooted. Due to this, her origin has been modified and revised several times. Several common details remain the same, though: Kara Zor-El is Superman's teenager cousin, born to Zor-El—Jor-El's brother and Superman's uncle—and Allurain Argo City, a Kryptonian city that survived the demise of Krypton thanks to an energy bubble-like force-field erected by Zor-El. When Argo City was also being destroyed Kara was sent to Earth where she met her cousin and eventually donned the mantle of Supergirl.
Baffled,Superman? Let me tell you my story, as my parents told it to me! When Krypton blew up, you were not the only one to escape alive...— Supergirl