Sandy Tanaka

 was junior navigator on board the Pollyanna. Sandy had been trying to decode a looping signal that she had picked up. Clara Oswald used the TARDIS to translate the message, which turned out to be a warning about the Umbra from the scientist that had trapped them in the Sun. She guessed that this message "might have been bouncing around inside the chromosphere for millions of years". When one of the Umbra's tendrils caught Clara Oswald, Sandy used a fire extinguisher against it to make it release Clara. (COMIC: The Eye of Torment)