Watching a movie with her raises her affection bar and only needs to be done twice to max that bar, if I remember correctly. For things to progress you need to raise her Desire bar too, which happens by going to the bedroom (hint, its not clicking on the bedroom door as I was trying at first, its using some navigation boxes that appear near the "roof" of the main room, in the topmost part of the screen).
Once in the bedroom and during the evening timeslot, you have the option to handcuff her, raising the Desire bar. Once both bars are maxed, Love stage will increase and more opitons will be available