Very risky. That’s the situation created by Hina when she opened up the curtain as well. At any moment, even if the cuck beyond the window couldn’t get a clear picture of what was happening inside the room, the possibility of him making a scene that Uncle and Auntie could pick up downstairs was high.
But knowing Ogawa who rarely showed that he possessed the balls to do something, Hina probably banked on that fact which gave her the confidence to pull this devious plan off.
Besides, for the girl, as long as he would be tormented by watching this scene, that would be more than enough to satisfy her thirst for revenge.
Was it similar to how Satsuki felt for Sakuma before I fixed that for her? Maybe… Nonetheless, instead of getting more turned on at the thought of Ogawa being aware of how far we’ve reached in our relationship, it’s more of a bittersweet revenge to show him what he threw away.