Not sure if this is mentioned other than Dev wrote shortly about new Diane Monday/Friday event a while back, can't recall post number and too lazy to back track reading all posts..
Anyways, after a lot of playing I finally found out how to see this:
Diane Repressed Mother (Latest AT)
Diane Lust high (not sure how much, I had it 100%, to get it there do NOT sneak peak at her masturbating in her room during the day times!)
Monday 22:00 Living room, check on Diane, ask if she is alright and go strait to Your Room.
Your room 22:00 go to sleep. You will be woken up for a new scene.
Friday: repeat steps from Monday, now you get the last part of the scene.
Note: Be sure to have room for at least 2 topics, as the last part can drop 2.. one being a new one called "Face Sitting".
It was mentioned to follow Diane around during those days, which I think is important, because each encounter makes her more intoxicated and she has to be hammered at 22:00
So during Monday and Friday, start following her around the house from 11:00 or 12:00.
You don't have to do a conversation, but be sure to have an Alcohol topic for dinner at 18:00 and use it to poor her some wine with the meal.
For the Friday you will miss out on the Becky and Co. party, but hey there is always another weekend right?