Hello, my friend.
Just read the latest updates... I'm so sorry about the news your sister received. All this must feel a bit unreal to both of you, and you are handling it extremely well. I am glad that Mary Ann lets you be with her and support her through this, given her generally very independent spirit. The power of support (both on the side of the giver and receiver) is definitely something that is not easy to imagine before experiencing it first hand and she has someone outstanding to experience it with in the current situation.
I hope for the best possible treatment approach for Mary Ann.