LEGO fansite Brickset has discovered a LEGO Dimensions instructions booklet for Supergirl, that has since been removed from the LEGO site.
This corroborates leaked video footage from earlier this month that showed Supergirl and Green Arrow running around in-game, leading some to speculate that they will feature in the next round of LEGO DImensions sets.
The fifth and final of the original waves launches next month featuring Lloyd from Ninjago, Bane from DC Comics, and Slimer from Ghostbusters. Whether these new DC characters will feature in a Wave 6 for the game or perhaps lead off a possible LEGO Dimensions 2 has yet to be announced. Perhaps we'll learn more in the lead-up to E3 in June.