You have asked one of the most difficult questions we all struggle with when someone we love is faced with the dx. There are many many postings here that I think would be of some help.
You need to remember though, someone she loved and trusted, left her at life changing point in her life. We can only imagine what she is feeling now. She needs to have her space. Her good days and bad days - they are about her and what she must face each and every day. She is, I am sure, probably thinking more of how this illness will affect everyone else. What it's taking from others. Does not want to be a "burden". We know different. She knows it's hurting you. You must be patient and make sure you support whatever she needs, or wants. You don't know what is best for her, she does. All we can do is research, research and more research, look for support for ourselves and hold thier hand when they let us. If you make this about you, it will never work. You will end up tired and frustrated and it will be too much for you to handle. This is something those of us on the other side of this disease must accept. We will never understand completely what is happening emotionally to those dx. Support her decisions and don't ever - ever say to her YOU are just trying to "help". "What can I do?" How can I make this easier for you?" She has enough to think about without worrying, once again, that she has become a burden.
This isn't easy. Coming here was a good start. She doesn't have the answers as to how you deal with this. You can cry with her, share her anger, fears, good news, bad news. She's fighting to survive. She needs to know she doesn't have to worry about you. Though she will anyway. She needs to know, you will be there when she needs you to be. None of us are perfect - that's for sure! We have all made mistakes. We all stumble through the emotions of what to do and what not to do. That's why we search for a place like this. ~~I share things with my husband that I find here. About same situations and what some of us here go through. Sometimes he could care less, and sometimes he asks how Patty and her Mom are doing.
Please don't think I was preaching or lecturing - The fact you came here, wanting to understand, is really huge on your part. You have know idea how much searching something out like this shows how much you care. You can find alot here. And other places as well.
Just know, we all pray for each others strength and well being and mostly, to keep hope in our hearts each and every day. God Bless.