@ GlennM
'If getting water for sanitation was an issue, it is extreme to walk a half mile either way to do so.'
The issue with the tent site is:
The whole group needed running water badly to avoid the risk of dehydration during in the cold night in a dry air environment.
This is not an opinion or a view, but a fact for survival in a cold climate with dry air: every exhalation moist leavest the body while no moist will be inhaled.
Nowadays this risk is handled by melting snow every hour or so on small petrol burner, like the 'Dragonfly or 'Whisperlight' by MSR or models by Optimus.
Before arriving at the tent site, the group had made the ascend of 350 m elevation over 1 kilometer from the storage to the tent site, with 25/20 kg rucksack and skis and ski poles in their hands.
This is an ascend of 35 percent on average, so many parts are steeper.
This kind of climb consumes a lot of energy over some two hours or so.
By sweating and exhaling the group members had to replean their water level.
After doing so, very probable their waterbottles had mostly emptied.
Suppose these facts resemble the situation of the group while preparing for the night at the tent site, it makes sense that:
- several group members had descended to the ravine - as place nearby - looking for running water
- Lyudmila had one of these group members, so she had been able to clean herself.
Additional remark on privacy:
- Lyudmila had been found in the stream flowing in the ravine
- the den had been several meters away
- personally I assume that Semyon had been near the den site and Lyudmila near the stream when the blast wave had hit both.