I'm so sorry to hear about your pain. I know what it's like to think that she isn't going to come thru this time.
My mother just passed 5 days ago and I had this internal thinking that she wasn't coming home from the hospital. I took the time to whisper whatever I needed into her ear. Just make sure that you don't leave anything left unsaid. Even if you think you may have nothing left to say, there may be that one thing left.
It makes me sad to hear that your sis is that young. Your sister knows that you have always been there for her, I can tell because she let you be the "meal time watcher". That is something to be proud of!!
I will keep positive thoughts in my mind for her and hope she makes it thru ok.
((((((hellishlygood))))))