I agree that the van is empty (after looking much closer several times).

Some hands are already on her at the time. I think she had agreed to go quietly and not make a spectacle in exchange for something (like speaking appearing at the event instead of missing it), but this was the moment she was overcome by the gravity of what would happen next, after she got in the van, like she'd never see the light of day again, and only see the TV camera in a controlled studio in GITMO.