Sonya Khan was Yasmin Khan's younger sister. She lived in Flat 34 of the Park Hill estate in Sheffield with her parents Hakim and Najia as well as her sister. She was unemployed, (TV: Arachnids in the UK) and wanted her sister to move out of their house, so she could have her room. (TV: The Ghost Monument) The two siblings did not get along. (TV: Arachnids in the UK)
When Yaz returned to Sheffield after her involuntary adventures in time and space, Sonya teased her sister for bringing back the Doctor and Ryan to their flat for tea, claiming that she had no friends.
She was keen to flirt with Ryan after he clarified Yaz was only a friend, and claimed Yaz had no love life, due to being married to her job as a police officer. Yaz retorted that unlike Sonya, she had a job.
She celebrated her grandmother Umbreen's birthday party at the Khans' flat. Umbreen gave Sonya a present that Sonya's grandfather once gave her. While Umbreen was giving a present to Yaz, she remarked that Yaz was her favourite granddaughter. This caused Sonya to be sad and shocked. (TV: Demons of the Punjab)