Like her cousin Kal-El, Kara Zor-El is a survivor of the destruction of Krypton, escaping in a spacecraft of her father's design. The craft put Kara into a state of suspended animation and followed the course set by her infant cousin's craft. However, instead of the trip taking a matter of seconds, like it had for her cousin, it took decades. On crash landing on Earth, Kara suffered a truly rude awakening as her powers manifested almost immediately. Wrestling with those powers, she was astonished to meet her cousin, now a grown man. The worst shock, though, was to come: Kal-El told her that they were the only survivors of Krypton. She was nearly overwhelmed by despair, and hated the alien world she was trapped on. Fortunately, Kara discovered a resilience she didn't know she possessed and is now dealing with her grief and learning to love her new home world.
As she is a Kryptonian, Supergirl possesses all the powers of Superman. However, not having grown up with those powers, and having a more fiery disposition than her cousin, Supergirl's use of those powers tend to be more forceful than Superman. However, she still possesses the same moral code of Superman and will avoid using lethal force.