When you go to bed with Christa try to "Mess with her" or "Have Fun with her" I don't recall exactly how its written, then you'll have a "Touch Option" on her eyes, thats when the blindfold goes into action.
I guess it only completes the "???" when you do it WHEN the story kinda asks for it, if its "out of time" it doesnt complete it somehow, maybe something fixable.
