They could find a way to jump universes and visit her Earth to enact revenge for her efforts on Earth-1.
The first is that the Dominators who turn up on Kara’s Earth will be the same that Kara helps fight in “Heroes v.
It stands to reason that Kara’s powers will be instrumental in the good guys of Earth-1 saving the world.
If she is the game-changer, and if the heroes drive the bad guys away without wiping them out, the surviving Dominators may come to consider Kara a nemesis.