Turns out that even though the characters can't read any written text or watch any movies pertaining to them... well, the most important thing she says, in short, is this:
Wicked Witch wrote:So I looked around for summaries of this film. I found, among other things, this: http://en.wikipedia.org/wiki/The_Wizard ... (1939_film)
It seems to be a story about me! And Oz! And every summary I read celebrated my villainy.
This has hardened my resolve to return home, and reaffirmed my belief that it is possible.
In short? They can't read or percieve their canon, but they CAN READ THEIR WIKIPEDIA PAGES. This has already been successfully tested on both Sweeny Todd AND the Wicked Witch.