The first thing I’d want to know is did this crew, and particularly this nurse, have any training in hoist operations. It’s not ordinarily something life flight crews train for, AFAIK. There’s a difference between medical transport and full fledged SAR. If you’re not trained for the latter, attempting it is asking for trouble.
Boy! That’s lacking a bunch of information, isn’t it? Was she on the ground and actually assisting the person they were looking for or did she fall from the helicopter or from the helicopter’s equipment? Why is the NTSB involved?
She probably wasn’t clipped in properly to her harness. It was dark and she may have overlooked something.