I happen to agree with MaryCas.

By this time Sonny has been dead for several years and Connie/Carlo have had their second child.

By giving Carlo a prominent position within the Family ("Carlo, you grew up in Nevada. When we make our move there, you're gonna be my righthand man."), Michael and Vito have already lulled him into believing he's trusted and relieved of blame for Sonny's death. He's pretty confident of his security.

By the time they want him to stand Godfather to the baby, Michael is basically Head of the Corleone Empire. I agree that the still mousey Connie is intimidated by her brother's prominence and simply afraid to approach him about the baptism, concerned he's now much too busy to consider such a thing.

It isn't until after Carlo's death that Connie could ever have the nerve to confront Michael the way she does at the end of the film.

Apple