I haven't liked Cora for a while, but I actually don't blame her for this one. If you look at it from her perspective, there is a man who has admitted soliciting a prostitute in court, up acting the family man beside his wife and kids. Throw in the fact that she believes that her daughter is basically being preyed upon by men like him in order to fund her addiction then I actually understand why the perceived hypocrisy might irk her enough to want to lash out at him, without even thinking. Remember, she has her own relationship with Stan at risk here too - so clearly she's not rational at that moment.
The real villain in this piece is Ian, who is just standing there letting his ~friend be humiliated and his reputation pulled apart in order to save his own cowardly skin. The guilt trip he laid on Mick in the first place was bad enough, but this is just pathetic.