While watching the ostentatiously trashy new movie Supergirl, I could not help but think how the mighty have fallen. Or should I say, how the mediocre have fallen? Not being a reader of any iteration of the Supergirl comic books published by DC Comics, I cannot comment on their quality as compared to the subsequent screen adaptations, but I can say that the 1984 film version, with Helen Slater as Supergirl, was passably diverting and perfectly inoffensive: a piece of Reagan-era hokum somewhat redeemed by practical special effects, a rousing Jerry Goldsmith score, and, though the movie was a British production about a gal exiled from Krypton, its makers’ abiding belief that the Supergirl character represented a continuation of her cousin Superman’s commitment to truth, justice, and the American way.