In December 2007, during a routine training session with the children at the Institute, during which she was teaching the kids how to throw knives, the Institute was attacked. She and Mark Blackthorn left the children in the training room to investigate.
At the foyer, they joined the other Conclave members as they faced Sebastian Morgenstern and his Endarkened army of Shadowhunters. Along with Andrew Blackthorn, Katerina was forced to drink from the Infernal Cup and became a Dark Shadowhunter herself.
Whether Katerina died before or after the destruction of the Infernal Cup is unknown.