I'm so sorry to hear your news Rachel, it's always difficult to lose a loved one.
Please think twice before cutting yourself off from Rootschat, I've found as I know that others have, that it's a haven to get away from the real world. It is often easier to "talk" to people that you don't actually know and who you will probably never meet.
As to adding details of your grandmother to your tree, my advice at the moment would be don't until you feel ready. I didn't add my mother's death until fairly recently even though she died 7 years ago.
Whatever you decide, I hope that all goes well.
Take care
Jan