That's a long time to be in the water w/ no life jacket.
True, but if she had any survival training for water emergencies she could curl up into a fetal position holding her legs close with her arms and bob in the water and take breaths as required using as little energy as needed. The air in your lungs helps keep you bouyant and it is much easier (less energy expended) than treading water.
This position also helps you keep your body warmth to ward off hypothermia. I don't know if it will work for 36 hours though.
Prayers for the young lady and her family.
SZ