Agreed. That's my philosophy too: the movie is the movie and the book is the book. [/b]
Yes, the novel is the novel and the film is the film. I would not cite a passage from the novel to "prove" a point about the film, but the novel does provide detail and perspective that can be helpful. In this case, we can infer from the novel that Kay'd had plenty of time and examples to figure out what her old man really was.

This leads me to theorize that even though she knows that Michael is a mafia chieftain and no where near legitimate -- and that she knew all of this way before the Senate hearings -- the hearings struck her with one final thunderbolt: Michael can and has killed in cold blood himself. At that moment of the hearing, ALL her delusions are stripped away for good and she can no longer shy away from what she previously didn't want to face.
I really doubt that Kay had any remaining thunderbolts about Michael at that point. If anything, I believe she looked resigned at the Senate hearing--resigned to her (probably long-planned) departure from him, with the kids.
We've had many threads on Kay and how much she knew--or how much she deluded herself, rationalized, denied, hoped to change Michael, etc. But for me, the moment of truth came on the night of Anthony's party: First the statement about "legitimacy" while she and Michael danced; then that look that she gave him after the machine-gun attack. That look said it all. I think she had concluded before the attack that Michael was a Mafia Don and had killed with his own hand. The machine gun attack confirmed for her that he'd never be able to free himself from the Mob life--and that he didn't want to--and that his "destiny" was a mortal danger to her and her children.