The rationality of the decision hadn't occurred to me. It's possible to reach a place where we no longer have the capacity to decide.
I also hadn't considered the fear of the unknown, but knowing my mother in law, I would have been surprised if she felt that way. She scratched and clawed her way out of poverty, and felt there was so much more she wanted to do.
Thank you for the thoughtful response. It gives me even more to think about.