This is really frustrating to read over and over again. It has to be something extreme. I'm sure the comments have been removed but in the original thread one of the leading theories was that something happened regarding the youngest sister, since she stepped away from the sport at the same time. Beyond that it's either that "gray area" training turned into the black area, or that something like a grudge or disagreement turned into an active sabotage attempt. There are only so many movie tropes I can draw from here.