SPOILERS
the more you play the game and reread dialogue the more you will figure out your answer to that :) + i explained potion ending in a comment below, search for one that says "I found the potion ending a bit confusing" (in short she died) + yes + mary is cursed by the potion's side effects, she doesn't need to eat normal food (what does mary do every time hazel is eating? think about why hazel is hungry in the village sequence even though she lives w mary, etc. -- there's lotsss of little things hidden in the text) and in order to maintain herself she needs to eat parts of other humans, hence the hair etc