I think that Irene didn't know about it, the empress is playing the game alone cause Irene is just pitiful and incompetent. So, I don't think the empress shared her plans with her.
And about the perfume, I'm sure that the Empress is behind it. We could see how Cai were with the Empress before, and that she's like a mother to him. So maybe she just throw suggestions about fashion or something like that and the prince felt into her tramp
Why do I feel that she was attacked by the monster because of the scent of the perfume? Who knows if it was the empress who suggested Cailenden to choose that scent for the princess.