"Anonymous. I think where you have fallen down over there is to use the word the Leader. It creates the wrong impression from the very start. V. Waltz. I swing. The lady swings.No two swing at the same time."
Nope, you both swing at the same time, but the person going past will have a bigger swing, and theirs will end before the person on the inside. It would be an oversimplification to say that one swing happens before the other, because in fact they substantially overlap.
"But when it is time to go. That's what she should be doing."
She still must move in the context of what the leader has invited - he, and not she, is the one who knows as he initiates the swing if they will be dancing the back half of a turn or instead, or a back change step, and so it is he and not she who inflects it with the appropriate character to result in one or the other. She might suspect from the phrasing or place in the room, but that's not information that it's safe to act on. Of course if he invites and she doesn't go because there's someone in the way, he needs to pay attention to that too.