Of course she can cheat, but I find it impossible that a podium which is inspected prior to the show and is in full view of staff could contain a secret device out in the open and Trump and his people not be fully aware of it. Please, the guy, whatever his shortcomings is streetwise and not a fool.
A backlighted LCD (sans the polarizer/resolver) would be just a lighted panel — even when viewed though a polarizer — until a signal imposed (polarized) text on it.