Mel Narda was a member of Earth's Anti-Terror Elite.
She had bulging blue eyes. Due to childhood injuries, her face and vocal chords were damaged and had to use a voice synthesiser to speak. That and her eyes earned her the nickname "Frog".
She was one of the trainees taken by Admiral Nadina Haunt on an exercise to an unnamed planetoid. However, Haunt was working with the Schirr and Narda was being transformed into one of them. The First Doctor was able to stop the process, and Narda's old injuries remained healed. (PROSE: Ten Little Aliens)