Let’s not rush to judgement..possibly, she “unhooked” herself?
Then why swallow evidence to that effect?
Pretty much impossible to do without the cooperation of the tandem pilot. You would have to climb into the control bar thereby releasing the tension on the hang strap, then unhook and drop.
She fell out of her harness. Likely the tandem pilot did not check to make sure the leg loops were around her legs. Even solo pilots have made this mistake. They have also failed to even hook into the glider before launch. Hang gliding is not very forgiving of such inattention.