Donna S

Donna S was an employee of Miss Kizlet whose Foursquare was found by Clara Oswald using face-match. According to her page, Donna also had a Facebook, and had had 17 check-ins. She used this information to discover where Kizlet's offices were.

On the orders of the Great Intelligence, Miss Kizlet reset her and all other employees to factory settings, and they returned to their true selves. (TV: The Bells of Saint John)

Behind the scenes
Although just off screen, the rest of Donna's surname is Shakesheff, and she was the art department co-ordinator for the episode.