I first would like to say how sorry I am. Death is never easy to deal with, especially when you know it's coming.
I don't know how you feel, but I can understand how much this hurts. I wish I could give you some advice, but in this case, I am at a loss.
--hugs-- If I were in your situation, I'd be a mess... You have more strength than I do.
The only thing I can think of for you to do is to cherish the time you have left with your grandmother. Continue showing her how much you care for her.
If you ever need to talk, feel free to PM me. <3