I just followed the walkthrough, and I think it reset halfway through, so I had to do it again maybe?
I know there was watch stuff on sunday, then watch sister change into expensive stuff, then talk to her, but DON'T talk sense into, as that resets the sunday events. Also watch her and Douche in her room sunday evening 2100 I think? When you catch Douche putting his dik in sis mouf tell Elena, don't stay and watch. You have to run the sunday peep shows again until you can get a picture of Douche Dik in Mouth. Then Elena come to room next morning and start queen of BJs event, which you have to finish along with all her other quest, before you can start photoshoots. Then you can talk some sense into Sis to keep her away from Douche. That is me best recollection, but it should be in the walkthrough.