If she isn't moving at all, it's usually because the leader concentrated on his own movement and decoupled from the embrace (i.e. he moves, but the parts of his body connected to his partner stay with her current position instead of moving with the rest of him to communicate how he's moving). If she's moving but doing something else, the lead is usually either noisy (the leader moves in a way that makes the follower respond in an unintended way), not well timed, or flat out completely wrong, i.e. the correct lead for what the follower actually does. What I unconsciously do most of the time is move myself, but I concentrate on "painting" a path for a point outside of me with my body. And, just like when you paint or draw, it's all influenced by the tactile feedback you get while drawing the path (when you draw with a pencil on a sheet, you don't actively try to trace along the sheet of paper, you use the feedback from the tip of the pencil to guide you. That's why you can't practice moves solo: the feeling of the feedback is part of the experience).