I was diving with a group during a boat dive. There was a newer diver and she did not look ready to dive. I had never met this diver. The dive master had to remind her to gear up three or so times. This was about a 70 foot wreck dive. I didn't feel she was ready but the dive master insisted on giving her a try. I decided to stay with them because I was not confident in her doing this dive.
I entered first followed by her. I told her to wait with me on the surface until the dive master went in and she immediately dumped air from her BCD'. I ended diving down and bringing her back up before she got too deep. She ended going down again with the dive master next to her and landed on her back, on top of the wreck. She just laid there. The dive master and I had to get her under control just to bring her up and end her day diving.
As much as the diver was not ready to dive and probably was not meant for diving at all, I blamed the dive master for not recognizing this beforehand. Somewhat scary overall.