I can't start a new event with cookies. the favor is 200+ and it seems like the relationship is already sexual, but nothing happens.
Hey, there also a couple of more triggers you have to fullfill that are basically progressing their story.
you have to see cookie's drinking event (the point and click one), have a drink night with cynthia and cookie and then see the event where cynthia is teasing you and cookie about 'something'. Hope it helps!