Oh that Saturday visit had me tearing up. I'm so sorry for your/H's loss and I'm glad that your DD's last visit with him was a sweet one.
I don't know if this will work at her age, but maybe pick out a bright star in the sky and correlate that to her grandpa? I've never had kids or had to explain death to them. I was 5 when mine passed on my mom's side and I don't remember it at all, don't know if I chose to forget it or legit was too young. However I do remember times before it with him, only the good times oddly enough.