Supergirl gets the cover feature for Action 258 (Nov. 59), a story by Binder and Mooney.
Supergirl will get the cover spot far more often than any other back-up series, largely because it was often possible to include Superman in the cover image for the story.
Supergirl meets Krypto in this story, to Superman’s anger. He is upset that she revealed her identity to the dog, who might give it away. Yes, the dog might reveal Supergirl’s existence to the world. Somehow. At any rate, Superman exiles her to a far off world.
After a while there, Supergirl receives a message from Superman that she is to return to Earth for one day, to avoid a kryptonite storm that will hit her exile world. She comes back to the orphanage, pretending to have been lost in a swamp for a week.
The press show up, questioning her about her story. One reporter in particular seems intent on exposing her lies, but she turns the tables when she admits that she is Supergirl. The reporter is Clark Kent, who is dismayed that she revealed herself so easily. But Supergirl explains that she only did so once she figured out that Clark was really Superman.
The entire series of events, right from the meeting with Krypto, is revealed to have been a test, which Supergirl passed with flying colours. Ironically, Superman had been planning to reward her by revealing his identity. Too late.