As far as we know the CBS Supergirl pilot hasn't actually started shooting yet, so this pic was most likely taken at a read-through or something -- meaning Benoist and Slater are probably not in character. Still, it's a cool first look at Supergirls past and present together.
So far the cast of Supergirl also includes Laura Benanti as Alura Zor-El, Chyler Leigh as Kara’s foster sister Alex, David Harewood as Hank Henshaw, Calista Flockhart as Cat Grant, Mehcad Brooks as Jimmy Olsen, and Dean Cain in another mystery role.