A Production Diary compiled by David J. Howe, Mark Stammers and Stephen James Walker from contemporary memos and correspondence [REF] notes that producer John Wiles and story editor Donald Tosh employed Sara Kingdom as a "short-term companion..[to] be killed off at the end of [The Daleks' Master Plan]" [REF].
Jean Marsh had previously appeared in Doctor Who playing King Richard's sister, the Princess Joanna, in The Crusade.