It just occurred to me that Jenna Coleman playing Clara is just another one of those cases where you have the same actor twice as different characters in a tv show
Except they actually solved the problem
George this is Doctor Who we’re talking about
They’re like the kings of using actors more than once and then smoothing it over.
It was Martha’s “cousin” in Doomsday. Donna was, well. Amy was wearing facepaint. The girl who played Gwen Cooper in Torchwood has a cameo in the 1800s-her family had been their “for centuries”.