In Stephen King’s epic novel, Nadine goads her lover into killing her by taunting him about the members of the Boulder Free Zone making their way to Vegas, but the adaptation arguably gives her more agency as she uses the glowing stone Flagg gave her to smash a window in the hotel penthouse suite and leap out.
Of course, Nadine does eventually figure out exactly what Randall Flagg is/represents – but by then it’s too late for her to be saved.
It’s not until she recognizes that she is preparing to give birth to a monster that she comes to terms with being nothing more than a womb to sire evil’s child.
Both stories essentially end the same way, though the CBS All Access version does rub some extra salt in the wound by having the scene where Nadine’s severed head is presented to Larry on a platter.