She was actually swimming with a group of people. They spotted the shark and the orange boats went and tried to pull everyone from the water. There was actually another person in the water that the shark bit first. They didn't reach the woman who initially got bit in the video right away. When they came around to attempt to pull her up afterward, the shark saw the boats as a competing predator and tried to win its selected 'prey.' This woman lost her leg as a result, the shark pulled it off thanks to their 'rescue attempt' to get her into the boat. You're not supposed to swim out in open, deep ocean. Whoever let these people swim out there is a jackass.