You could become a prop for her. Pu/pd at this age is more of just the pd part. So you could reassure her, and then just continue to lay her down once she is calm. My ds never really went for this though as he would just get more upset if I stayed in the room with him. So I used the walk in/walk out. I would put him down and leave, and then once I heard him getting upset I would go back in reassure him and leave again, and I would do this over and over again until he no longer became upset once I left. I never waited for some predetermined time to go in, I just listened to him and went when I knew he needed me.