I'm so sorry about your grandmother and your pain. I completely understand.
I lost my great grandmother to cancer just last month. We're a very close family, and it was an especially difficult loss. She was diagnosed with cancer and left this world only three weeks later. The one thing I'm thankful for is that we were able to have a very honest, private conversation while she was still able. That brought a lot of comfort when she actually passed on, because I knew she was at peace with her God.
Again, I'm so sorry and you have my prayers.