Turned her air off and then turned it back on later? This doesn’t pass the smell test and, unless there are witnesses, I call b.s. He would have also had to completely deflate her bc to make her sink so fast that the divemaster couldn’t reach her.
I am a trained rescue diver (I weigh 128#, so don’t expect me to drag you up the ladder on any boat.)
Or he could have overweighted her. From the picture she is already on the bottom when the DM sees her in trouble.