Mom hasn't eaten in 4 days. How much time does she have?

My mom is 101 years old and living in a nursing home. She has lived there for 2 years now, moving in after a stroke that left her paralyzed. Despite being paralyzed for the past two years, she has been pretty "mentally there" for the most part, (knows who I am, knows where she is at, able to have a conversation, etc). Ever since I have moved her there two years ago, I have gone to visit her everyday. Some days she would talk my ear off, on what I call her "good days" and other days she would just sleep the whole time on her "bad days". This past month, she had been having more and more "bad days". So when I went to visit her 3 days ago, and she was having yet another "bad day", I didn't think much of it until her nurse told me she wouldn't eat the night before or that morning. I gently rubbed her arm and asked her if she would eat something and she opened one eye and shook her head. I did the same thing the next day and got the same response. Yesterday and today, I got no response at all.