J.
My mom can still recite my brother's favorite book as a child.....he's 34 years old. Personally, I would put a boundary at certain times. I would do this by giving her 2 other options to choose from; "we aren't going to read anymore but you can either do this or that (things that she used to enjoy for example. At bedtime, 2 books, end of story. Other times that work for you, read more.....
Just an opinion....