freewill, you're not "letting this happen"....the world is full of chaos...we cannot control the destiny of others.
Perhaps it is her time. Maybe her body is shutting down. Everyone makes choices and they have that right, no matter how much we think otherwise....when we intervene we take away that right and make choices for them, essentially playing god.
there's no hope in that, only disappointment.
you do what you can do by talking to her, make an attempt at getting her some food but then accept what happens.
you or I do not control life on earth, only god does.
you're a good person for caring but don't beat yourself up on this.