Supergirl, or Kara Zor-El, is Superman's cousin who arrived late to earth. In the mainstream DC universe. Power Girl is Kara Zor-L, cousin to the Superman of EarthIs Power Girl Supergirl's daughter? Contents[show] History Origin Power Girl is the Earth-Two counterpart of the Kryptonian Supergirl and cousin to Kal-L, the Superman of Earth-Two. Possessing.