ok, immediately Family Matters by Rohinton Mistry came to mind. It is simply a beautiful novel. The setting is in india, and it's about a family there. The novel primarily focuses on the different characters of this family. In the middle of it all is an elderly man, who is the father and grandparent to the other characters of this book. This man is living with Parkinson's disease, and has a broken ankle, so basically he is bed ridden. You feel a great deal of emotion towards him, and you sympathize with him because u know that he really does not want to be a burden to his family.
I can't recall exactly how the story goes (cuz I read it some time ago), but do take the time to look it up.
Your mother might be able to relate to the Parkinson's patient, and also draw upon the more fortunate aspects of her life. As this novel's main theme is about family and the love and our duty to one another, she may feel some hope in her own situation.
This is such a wonderful book, that I'd even recommend you to read it.
Best wishes to ur mother. And I hope my recommendation helps
