Kym Howaska was an agent of The Company. She pretended to be someone that Zoe Heriot had met during her travels with the Doctor, in attempt to jog her suppressed memories and get information about time travel for the Company. (AUDIO: Echoes of Grey)
When this failed, the Company arranged for her arrest on charges that carried the death penalty, threatening to have her executed unless she could prove she had travelled in time and share the secret of time travel with them. Kym took her to Space Station Artemis, but then helped her escape, sacrificing her life to do so. (AUDIO: Second Chances)