Donna S

You may be looking for the art department co-ordinator whose actual Foursquare was used in the episode.

Donna S was an employee of Miss Kizlet whose Foursquare was found by Clara Oswald using face-match in 2013. 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.