Epitah is a planet of unknown type, that is being mentioned by Gaige through her dialog at the beginning of The Holodome Onslaught DLC for Borderlands: The Pre-Sequel. According to the same dialog, Gaige and Axton were sent there by Lilith, shortly before the interrogation of Athena, to hunt one of the Eridian vaults shown on the map in the final cutscene of Borderlands 2. It also turns out, that on their way there, they encountered Aurelia. And since she was helping Jack in his rise to power just like Athena did, they were probably ordered to kill her. However before they do that, The Watcher saves Athena from execution and tells other Vault Hunters about an upcoming war. Lilith then orders Axton and Gaige not to kill Aurelia and safely bring her back to Sanctuary as another ally for an upcoming war.
It is however unknown how did Aurelia get on the planet Epitah herself.