While there is no good explanation sometimes for why we have to go through the things we do, there is always a chance for someone like you to become a stronger person because of it. Sometimes you do all that you can and still realize that in a way you have zero control.
Our thoughts and prayers will be with you and your grandmother during this time in hopes of the most favorable outcome. As for what you can do, pray as if everything depends on God and then continue to do everything you can to make the situation better as if everything depends on you. With this kind of attitude, you'll come out the other side of this someday better for having gone through it.
I admire your compassion and willingness to help loved ones in need.