grief in child cancer survivors

I am the mother of a four-and-a-half year old with neurofibromatosis type 1. She has survived an aneurysm, a stroke, brain surgery, an optic nerve glioma and 15 months of chemotherapy, from age 18mths to almost three. Her tumor was considered to be benign, but was inside the skull and growing and threatening her eyesight. Her prognosis is very good. My mother was having chemo for metastasized breast cancer at the same time and the two of them were "chemo buddies" a ghastly attempt to find some humor in the situation. Mom just died in October, and my little one is having a really tough time dealing with it. She is exhibiting a lot of anger, nightmares, clinging to me, terrified if I get even a cold. She seems to think that we are keeping grandma from her some of the time, and that if she is cruel to my aunt, whom mom appointed a substitute grandma, that grandma might come back. I'm afraid that she will figure out that she had the same treatment and become afraid for herself, although Hospice assures me she won't. She doesn't seem to fit the profile of the average toddler. Her experienced haved matured her in an oddly uneven fashion. Has anyone out there dealt with a similar situation?