One issue I first encountered few months ago was this frustrating issue where Willow's temperature in caves automaticaly decreases when it starts raining. She can ever wear protection, but when she has some wetness, the temperature just starts to fall down below freezing point, eventually killing her. She even had above 50% of sanity, so its not caused by her disadvantage.
I was in Ruins when it started raining and because I was low on wood, my fire went out some time later, so I could only try to reach the surface before she dies. I checked moisture (5/100) and sanity (70-80/120).