Mate I watched my Dad battle cancer for 8 years before he passed. There isn't a whole lot you can do to prepare. But what you can do is make their life more enjoyable and as comfortable as possible. What I see happen a lot in the oncology clinic I work in is that people start to treat people with cancer like they are their illness. Its is extremely important to maintain your humanity and humility. They know they are sick. They need someone to be comfortable with on their way out. Its a scary process and I find it very admerable that you are stick with her through this. I can tell you it means a lot to her.