S.C.
I'm sorry to hear of your grandmother's condition. To a little kid, the death of a dog might be as big of a deal as a person (of course, my teacher thought I had a brother named Alex, but it was just our dog who was my best friend until I was about 6 and started having human friends). Talking in advance is a good way to introduce the idea so it isn't such a sudden loss. Some of the suggestions I've heard are stating that our bodies break like sometimes a toy breaks and can't be fixed. Or that people are like eggs, sometimes the shells break, but the part that really matters, the inside lives on in heaven. We're going through this with my step-mom having cancer and I think it will be easier on my 3 3/4 year old because we've talked about death before (we have pictures around the house of my sister and father-in-law who've died and talk openly about them).