I'm pretty sure the CW wouldnt bother its pretty little head about any historical accuracies, because their audience isnt going to know the difference so it would be wasted. I wish they'd just go whole hog and have Mary waging a secret war against the vampire hordes, especially their leader, Elizabeth I.
Oh, you didn't know she was a vampire? It's so obvious in retrospect.
Throw in Cleopatra, Catherine the Great and (hey they already went there) Marie Antoinette, and you have the makings of epic entertainment. Of course they will all be 15 years old, played by 25 year olds.