No, you are *not* a horrible person, salukigirl.
You're frightened about something you don't understand. And that is very normal.
It sounds as if your grma has alzheimer's disease. It's a disease that attacks the brain, and it's the most common type of dementia. It's easily found on a google search, where you can learn about it. If you do decide to visit, here's a list of things to do with people who have alzheimer's:
http://www.alz.org/living_with_alzhe...activities.asp
I hope this will help make your decision easier. Understand, your grandmother has a disease. She's still in there; she still loves you. But, her mind is being destroyed. But, just like every other human being, she still needs love.
And so do you.

Peace!