JW's have been known to watch the obituaries and send messages to the families of the deceased. I've heard of cases where they hang out at cemeteries and hand out pamphlets. The first thing that came to my mind when reading your post was that this woman followed you from the hospital or was handing out Pham-lets at bus stops and gas stations, or wherever people can be snagged incidentally and or by surprise.They do this every day of the week in every town and city. It's only a matter of time before they run into someone who is having some sort of personal difficulty.
Why would God wait until your grandfather was ill before he reached out to you. Why would he send someone to you at a gas station when there are thousands of terminally ill children be laying in hospitals ?
My father didn't get to become a grandfather because JW's talked him out of having a blood transfusion when he was studying with them. They don't allow it even to save their own children's lives. He died in agony upholding their rules and afterward, they wouldn't allow his JW family to use their Kingdom Hall for his memorial service because he wasn't a baptized JW yet.
Do lots of research before getting involved or at least wait until your grief has subsided and you are thinking clearly. They prey on the vulnerable because the vulnerable are prone to engage in magical thinking.