Dealing with a family member with cancer is not easy, especially when it is with a child. I know first hand from when my family lost my sister to lukemia years ago. She got the cancer at 2 1/2 and she passed at age 6. Its not easy dealing with the cancer, the treatments, and not know which is worse, a bleak prognosis or it coming true. Never is easy. But the best thing to do is rely on your support system and hope for God to give a miracle. So far, He's given you more time that her doctors has reasoned.
As far as your support system goes, it sounds like you found a good one with FT. You, your granddaughter and your family will be in my prayers.