Auntie Cordoolia was a female tawny owl. She was the aunt of Asio Bardwing who was related to Uncle Wilfrum. Mad Maudie Mugsberry Thropple learned of her through Asio, and pretended to be speaking to her when she 'read' Asio's claw.
The forgetful owl didn't remember that he had told the hare about his aunt, and thought Maudie's conversation with Cordoolia to be real. Auntie Cordoolia was only mentioned, so nothing else is known.