WAG: She tried to pull her legs through her arms to get her hands in front of her, maybe crouching atop the bench to do it, got them at least partially through, but lost her balance in the process and fell, maybe a somersault, pressing her neck onto the section of cuffs (a chain?) between her hand(s) and the bench.
The part that has been overlooked, over and over, is in the original article cited in the original thread:
Still difficult to kill yourself that way but I think it is a little more understandable how it happened. She tried to get the cuffs out from behind her and got the chain caught around her neck.