Speaking as a follower, you still need lead and follow in a routine, and not just when you break from the routine. Even when she knows the steps down cold, she has to dance as if she doesn't, that is, her movement still needs to be a response to the lead's movement. Believe me, it's a challenge to know a routine and never anticipate the next step. As my coach describes it, on every step the lead initiates the movement and the follow responds (and a really good leader then follows his follower's response). That dynamic needs to be happening at all times, regardless of whether one or both people know the pattern that's next.
And by body lead, I didn't mean the bodies need to be touching, just that the movement begins in the lead's body. How it's communicated to the follow depends on the dance, usually through the lead's frame. But a follower can follow a body lead visually in a Latin dance when the partners aren't even touching.