You don't have to rollback far at all. Literally to the onset of this encounter, meaning right after mc leaves his room after his pc begins updating. Click on the sis' door, and instead of clicking on her initially, try the laptop on her bed and/or the dildo underneath her nightstand on the left hand side of her room first. After that, I believe you can speak to her which should get you past this bug.
I've never understood how this keeps coming up because I never encountered it myself, and could never duplicate it. Very weird considering I've played this game many times for all the different routes possible too. My only guess is perhaps you're playing with a mod (which might cause issues), something I've also never done?
I guess it doesn't matter atm, considering the current state of the game, but it kinda sucks it keeps plaguing so many players. Maybe putting a heads up in the OP might prove beneficial here.