Yvonne Hartman was the head of Tourchwood One at the time of the Army of Ghosts. She was in charge of opening the Void to start the ghost shift and let the ghosts into the world.
She was confident in herself, claiming that anything alien is the property of Tourchwood and that someday Britain might become an Empire once more.
When the ghosts were revealed to be Cybermen, she was captured and was one of the first people to by converted into a Cyberman. She did however to regain control of herself and in her cybernetic form, destroy several Cybermen who were trying to escape into the Void.
It is unknown if Yvonne is still a Cyberman or if she was sucked into the Void.