Once the belt is around your neck, very tough without training. Best defense is pre-emptive: know surroundings and exit routes, periodically glance your blind spots as you walk, avoid walking past places attacker can hide, basically keep them from sneaking up behind you. If you felt the belt before it was taut and you realize what’s happening fast enough (a big if), you could try to prevent it from tightening by grabbing the attacker’s wrists and/or the belt, taking a step back with one foot to avoid losing balance, pivoting so you’re facing them instead of being dragged backwards and then use any weapons or techniques you have, if you know how potentially you can force them to cross their wrists and unbalance them but again this last item would be hard without training. Recovery gets significantly more difficult once the belt is tight and they’re pulling you off-balance or you’re on the ground, but in principle you want to regain balance and leverage (whether from a standing or sitting position) so you can counter-attack and run. As she’s being dragged, if she sits and becomes dead weight to slow the dragging while grabbing the belt to relieve pressure on her neck, she has an opportunity to grab one of his wrists and the opposite ankle and unbalance him laterally, grab both ankles and knock him backwards, maim his Achilles tendon or calf or thigh muscles or dig her nails into his wrist to distract his attention from his grip. . .Some ideas just from looking at the video, but this is just brainstorming in answer to your question; would be best to practice with a partner at controlled speed to see what you can come up with that your muscles are going to remember in a real situation.
Also tuck your chin as soon as you feel the belt.
There are definitely criminals that are now going to try this with a belt. It’s pretty effective. It clearly is not the first time this guy has done it.