I agree TB that Connie had several things to reconcile in her mind. She had led a sheltered life as the Don's daughter either not knowing who he really was or denying it and benefiting from it. She was also helpless to prevent Carlo's murder. She had been lied to by her brother regarding it and belatedly came to recognize just who her brotehr was ("You cold-hearted bastard" and "That's your husband" and "Read the papers"). Just those two things would have been a mountain for her to climb emotionally. Then the murder of her brother by her brother in which she unknowingly assisted. Madonne! Yes, to keep her sanity, she convinced herself that Fredo drowned. And, yes, she was also feeling guilty over Sonny's murder and yes, I can see Michael having some negative feelings toward her because of it and her knowing or feeling it. Thus, she came to completely identify with Michael("Do it!"). It was all a defense mechanism.