I'm on the fence about whether Connie's development is realistic or not. By GF3, Connie apparently has ambitions to preserve the Corleone empire even if it means doing away with traitors and enemies by serving up poison cannoli and directing Vincent to commit assassinations. I know GF3 takes place in a more modern era, but is it realistic, even in the 70s, for a woman to be so involved in the murder and retribution aspect of mafia business?
How is she even privy to the fact that Altobello is a traitor and that Joey Zasa is dangerous? Why does Michael allow her to hear and see so much, yet berate her for leading Vincent to kill Zasa? And if Connie has such ambitions to keep the crime legacy going, why does she champion Vincent as Michael's successor and not one of her own sons? (Granted, though, she may want to protect her own boys from the dangers.)
Where and how does she get this ruthless drive in her advancing years that leads her to care who Michael's successor is? Why not let Michael handle it? When Connie evolved from jet-setting rebel to sister penitent in GF2, it felt real; it was believable. It's just my personal feeling, but her next step to "co-don" in GF3 feels manufactured and unnatural.
Then I read olivant's post about Connie's possible Stockholm syndrome: her psychological need to identify with Michael, the natural dominator. Perhaps by immersing herself in Michael's business, she wishes to numb herself from the moral aspects of crime and killing until they're second nature and "strictly business" to her, just as they were for the men in the family. To hold on to her sanity, she must erase -- or turn a blind eye to -- the pain of losing Sonny, the pain of losing Carlo, the pain of losing Fredo, the pain and guilt of her role (even if inadvertent) in those losses. And most of all, she can ignore the painful task of looking squarely at Michael and clearly seeing what he has become.
So now I can see why the film makers had Connie evolve the way she did, but...
Her actual committing of crimes still feels a tad phony to me. Her denial of Fredo's murder and her propping up of Michael as family saviour who has no need of forgiveness all ring true psychologically and are rightfully included in the film. In order to cope, she is in denial. But the film could have still protrayed her as being in denial while fully witnessing the evils going on around her without her actually committing them, which I think would have been more realistic.