RAVEN- My deepest condolences to you on the loss of your great grandmother- she seems like she was an astounding woman, sorry for your loss.
As regards this wack job of a " sister " bugging you- it's SO like JW's to not honor boundaries like this, totally inappropriate though when you are mourning your dear great grandmother's death . You handled it really well by just kind of ignoring her and letting her fester in her own emotional juices. No amount of reasoning will stop these types of JW fanatics from thinking that we are " doomed " - so the best thing is to not get into any contact with her at a later date. Totally avoid her intrusion into your life as she will try to make you miserable by what she perceives as " saving " you. In reality you'll save YOURSELF by rejecting any of her intrusions on your personal boundaries. I feel for you- I've dealt with JW wack jobs like this- it's disconcerting to say the least. You are handling it well. Keep on keeping on. Take care, and I'm sorry for your loss