Hi, I'm social worker in a hospital and help families deal with this all the time. I am sorry for the loss and stress your family is going through. I have a few suggestions that might help.
First, if her grandmother is in some kind of hospice program, please get in touch with the hospice social worker or bereavement counselor there, they can be of great assistance.
Second, your reactions have an impact, if you are cryng alot then this can be part of what is upsetting her. I'm not saying "don't cry", and it's ok (and even good) for her to see you crying, but use these times as an opportunity to get into a conversation about it, about how this situation makes you feel and welcome her to join in sharing her feelings. Let her know it is ok to be sad, and hurt and angry, but it helps to talk about it...and know for yourself that this is a grieving process, it takes time.
Third, she could be worried about death and illness in general. At 10 she is smart enough to learn that these things can happen to anyone in any family and may be worried about how these kind of situations can impact her life and immediate family. Kids often worry, what if this were to happen to Mommy or to me, what would we do?
Fourth, there are many wonderful books that you can share, even the Chicken Soup for pre-teen soul has parts that deal with death. Maria Shriver has a good book about "What's heaven", although it appears as though it's for younger kids, the concepts are explained simply and easily so a 10 year old can read on their own but not be too overwhelmed with the content.
Good Luck. She's lucky to have a mom who is able to recognize her needs and is looking for ways to provide support.