As an example of how far Supergirl's popularity has gone (or rather, marketing) prior to the Pilot, take a moment and Google "Jeb Bush and Supergirl".
Page after page after page of links on comments he made. To be exact, 1,280,000 results.
You can't buy this kind of publicity, which, astoundingly, is also being exploited for political purposes. All good for the show as far as I can see.