grief before death

my grandmother has been fighting cancer for years. recently they did a petscan and found out that the cancer did not do well with treatments she has had the last 3 yrs. she has been in stage 4 from day one and still to this day. they told her at this point the only thing they can is to maintain the cancer and she could live another 5 years, as long she takes of her self. I know 5 yrs is a long way off but just because they say 5 yrs does not mean we will get that amount of time with her. i feel grief because i know it is coming. I don't know how to deal the feeling of grief?

Just be happy that she's still here and that you will have time with her before she goes. I've been through this with both of my parents and know how hard it can be.