I agree with SB. I always thought that what she saw in the room with the men around Michael, and then the door closing in her face cemented in her mind that he did order Carlo's murder. It never occurred to me that it could have meant anything else, or that she believed otherwise after that. Because she wasn't completely stupid, either-- she knew the business he was in, she knew the way the revenge thing worked, so if he hadn't ordered that, who had?

I think she'd already believed what Connie said at the beginning, but when she asked Michael about it, she was desperately hoping for a different answer. Maybe when he said no, there was a moment of relief where she almost believed him, but then once she saw the way he was treated by those other men, I think she knew.