Try it yourself, as best you can. For example, I put myself in roughly the same position as Lyuda, and can feel the muscle tone that is holding my arms up. Then imagining my heart being stabbed while I am in this position, it seems like my arms would immediately drop and I would fall sideways. The only thing that makes sense is if she died, then some time later, someone else put her in this position, and rigor mortis and freezing set in, to keep her upright like this.
From another forum:
" ...Tumanov said Dubinina died while lying on back, and that was consistent with rigor mortis on her body - what in turn was inconsistent with how she was found. So the conclusion was she was repositioned after a death, and it happened more than 24 hours after it .....The way she looks as if she collapsed in that position doesn't line up with her chest cavity broken. It would be almost impossible to lift your arms up like that unless she received her injuries while standing."