I saw it too. It’s really clear during the up-close, slow-motion segment. Small metal object falls to sidewalk from right pant leg, then bounces as she’s being moved forward from the post she’s been leaning on. After it landed, it more than likely was kicked by someone alongside her or behind her as they were loading her into the van.
My opinion is that it doesn’t come from under her pant leg.
Slow frame shows it bouncing off her upper right ankle area just above the hem line. Likely its coming from under her jacket since it bounced backward to rest in front of that beam and hidden during the rest of the video clip.