Nice parallel: Connie asked Michael for a favor at the end of GF by standing godfather to her son. He complied--and whacked her husband. Then, after she finally got over it, she fell on her knees in II and begged Michael to forgive Fredo. He complied (sort of)--and whacked Fredo. The novel implies a an interesting Michael-type "moral" rationale and connection to the two events (even though II wasn't included in the novel): Michael wasn't being cruel to Connie because it was her idea for him to stand godfather to her son--not his. Presumably the same applied to her plea to "forgive" Fredo

Connie's reaction to Fredo's murder might have made an interesting addition to the end of II, especially since III wasn't envisioned at that time. But her conversion in III to Michael's loyal retainer, and her transformation to assertive family member, was credible. So was Michael's acceptance of her. I think Connie must have realized that Fredo really was a traitor and a danger to Michael--and in any event, Michael was her meal ticket for the rest of her life at that point. Michael probably sensed that Connie was accepting his rationale for killing Fredo, which probably helped him deal with his own conscience.