Death of a loved one is a very tender and spiritual time. My personal opinion is that unless the person who is dying has need of help getting affairs in order, then they don't require any kind of clear discussion about them dying unless they ask for it. You all just need to savor the minutes of happiness and joy that you feel while being together. Wait till she asks the questions. If she never asks and continues to change the subject, then leave it be and just enjoy her while you still can. If she never initiates the conversation, I doubt you will ever regret not having had this discussion with her.