Rose was an idiot at the end of the movie because of the Overlook
for a psychic "vampire" immortal that Rose was, she ended up being a total idiot by underestimating Danny and the Overlook.
Rose scoffing at the blood coming out of the elevator, she thought Danny and Abra were doing parlor tricks or something.
For an "immortal" that Rose was, how could she not know about the Overlook and its bloody history of the murders?