What does Grandma Lilah suffer with in the book, Half a Chance: A Novel?

Grandma Lilah has dementia. It causes her to forget things, such as where she is. It means she is able to do less and less for herself, and unable to do things like kayaking and going to the store without issue. It is tragic that Grandma Lilah should forget the things she loves and that are such a central part of her life.