What was the disorder that Annie Wilkes had in Stephen King's Misery?

Answer 1

She is borderline psychotic (progressing steadily into full-on psychosis as the novel/movie progresses). Even just 1/4 of the way through, the writer character (Paul Sheldon) has already voiced his concern (to the reader, of course) that Annie Wilkes is borderline psychotic:

"Because of his researches for Misery, he had rather more than a layman's understanding of neurosis and psychosis, and he knew that although a borderline psychotic might have alternating periods of deep depression and almost aggressive cheerfulness and hilarity, the puffed and infected ego underlay all, positive that all eyes were upon him or her, positive that he or she was starring in a great drama; the outcome was a thing for which untold millions waited with held breath.

Such an ego simply forbade certain lines of thought. These lines were predictable because they all stretched in the same direction: from the unstable person to objects, situations, or other persons outside of the subject's field of control (or fantasy: to the neurotic there might be some difference but to the psychotic they were one and the same).

Annie Wilkes had wanted Fast Cars destroyed, and so, to her, there had only been the one copy," (Viking Penguin hardcover edition, p50).