Helen Fitzmaurice

 was Lawrence Grainger's niece and Edward Grainger's cousin. According to Edward, his father considered her "unbalanced". Margaret Pollard's mother called her a "liability". She often had moments where she was unaware of her surroundings.

Helen had an imaginary friend, Ahnji, who was in reality an alien that had been trapped in a graphaphone. When he was freed by the Third Doctor, Helen was cured of her strange behaviour. (PROSE: Echoes)