You forgot Anneke Wills.
Apparently, Gatiss wanted to use Jean Marsh to play Sara Kingdom aging to death in a recreation of the climax of The Daleks' Master Plan, but the budget wouldn't run to it. Irony, really, considering she played the role all those years ago.
I've lived for over 2000 years, and not all of them were good ones. I've made many mistakes. And it's about time I did something about that.
-The Twelfth Doctor, Doctor Who: Deep Breath