In 2048, Polly had joined the classified Project Sub-Zero, where she was incommunicado to the outside world and had been genetically engineered by Dr. Patricia Audley's experiments to survive in the extreme cold. She was turned into a penguin-like hybrid. As a result, she failed to return home at the end of term, which concerned her father, George.
Clara Oswald later confronted Polly and informed her that her father was dead. Polly and the other test subjects were later released from their cell by Winnie Clarence and the Twelfth Doctor. (COMIC: Blood and Ice)