BM, it is just so difficult for us to accept a loved one's decision not to fight anymore. There is nothing that I can say to bring you comfort, I know that. Some people just decide to go it alone. I am a very social person who spills my guts but I also didn't want to tell people about my diagnosis until there was no choice. For me, it was really about not having to support other people through their reactions. You must trust that she will take care of herself by identifying what will give her some peace to get through this. She may also be in shock right now and needs to process it.
Please let her know that there are people thinking of her...and that I, for one, think that she is unbelievably brave in her acceptance and recognition of what she feels she needs to do.