Trefusis

Miss Trefusis was head prison guard of Broadfell Prison, which held Lucy Saxon.

Biography
Trefusis knew about Harold Saxon and was sent to collect his ring. (DW: Last of the Time Lords) She and several guards, as well as the Governor, resurrected the Master. The Master took her life energy as well as that of several prison staff. (DW: The End of Time)

Behind the scenes

 * The identity of the woman seen collecting the ring at the end of DW: Last of the Time Lords was a matter of much speculation until it was revealed to be Trefusis.