User blog comment:Rassilon of Old/Young Justice spoilers at Comic-Con 2012/@comment-800707-20120913022839/@comment-1038387-20120913113800

One of the points of COIE was making Superman the only Kryptonian again (that's why they killed Supergirl) but Power Girl was too popular, and she could be salvaged (unlike Earth-Two Robin and Huntress). But she had to be different. Though for the most part, it just wasn't brought up.