This is an interesting question. Others can correct me, but I don't recall anything that directly tells us what's going on in Connie's mind about these matters.
Now, Connie's outburst to Michael is:
Michael! You lousy bastard -- you killed my husband! You waited until Papa died so nobody could stop you, and then you killed him. You blamed him for Sonny -- you always did. Everybody did. But you never thought about me -- you never gave a damn about me. Now what am I going to do?
The book has very similar language. Note two things: (1) that she
doesn't say that she doesn't blame Carlo for Sonny's death; and, (2) the bolded language - what specifically is she talking about there?
My suggestion is that Connie is hysterical because she doesn't know what she's going to do for sex. In the novel, it seems that she's a virgin when she marries, but she proves to be a very sexual character, at one point literally begging Carlo for sex. Her situation is finally resolved by "filling her bed" less than a year after Carlo is killed.
So I would argue that Connie might actually have thought that Carlo was involved in Sonny's murder, but that having grown up among gangsters that was somewhat normalized, so that she could still be happy in bed with him, and that loss is what she's mourning when she confronts Michael.
