Why didnt i cry when my great grandma died?

I had loved my great grandma. But she had forgotten everyone, even her husband of 70 years. My great grandpas still alive. I know i'll cry when he dies. Anyways, one january morning, I was asleep in my room when my little sister walked in my room, threw a pillow at my face, and told me "Great grandma died." The first thought that came into my head was "WTF!?" But i never cried. I guess i thought as it to be untrue. I felt like she was still here. Like she never left. I felt it hard to believe that she left and was gone. We went to the funeral and everyone was cryingm especially grat grandpa. Everyone, except for me. I couldnt believe she died. I just stood there in my furry boots thinking "shes not dead, she cant be" or it least it didnt feel like it. I just couldnt accept the fact she was gone. Why is this?