Mom refuses to eat. What are reasons for refusing to eat or drink?

My mom has slowly stopped eating over the course of a couple months and has lost 130 lbs. Last week she was admitted to the hospital with Guillain-Barre. They put in a feeding tube this weekend, but since she passed her swallow test with flying colors, they want to remove the feeding tube. However, she is still refusing to eat or drink anything since being admitted. She will do the physical and occupational therapy, though. What are reasons for her refusing to eat? I feel like she is going to wither away and all the other work she is doing will all be for nothing.