I'm so sorry!! Is her husband also your grandfather? If not, he sure may feel lonely. Just keep in touch with him - help him grieve, but remember to grieve yourself. It's the hardest part of the healing process, I think. Remind yourself of how very much your grandmother loved you (and you her!) and that you have lots of caring people on this forum.
I lost my cousin recently - he had a drug problem and was so very dear to me. He had written about me in his journal that was next to him... I take great comfort in the fact that he knew, really knew deep down inside that I loved him so much - and that he loved me, too.
Take good care - we're all here and praying for you and yours!
Liz