Eiry

Dr. Mandibarch married Eiryka and the two created Mandy Jr. . Then the two went their separate ways, with Dr. Mandibarch becoming a villain and Eiryka becoming the permanent librarian in the Underbelly of Athlaca
Dr. Mandibarch tried to recreate Eiryka , and Eiry is the result. So Eiry is Mandy Jr. 's half sister.
Eiry is the registrar at the Academy
This character, their story, and their stat block can be found in the Adventurer Academy Staff Codex on DriveThruRPG:
https://www.drivethrurpg.com/product/329754/Adventurer-Academy-Staff-Codex-50-NPCs