I'm so sorry to hear that. It may not make you feel better, but please remember that she's had a long, full life, and I'm sure she knows how much she is loved.
I am very close with my grandmother, and I can only imagine what you are going through and how hard this must be. Im sure she feels very lucky to have you and your family with her during this time. My thoughts and prayers are with you and your family.
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"Deep down you may still be that same great guy I used to know. But it's not who you are underneath, it's what you do that defines you" Rachel Dawes, Batman Begins