M.,
Coming from a mother who has buried a lot of family members in the years that I've been a mother (only 7) it is important to listen to your daughter. She is 4. By the time my daughter was 4, she'd been to several friend and family members funerals and viewings. This opened the door to the conversations that have brought us closer together as a family due to our beliefs. HOWEVER, my daughter at this age prefers NOT to attend funerals or viewings because she doesn't like the sadness involved. No one extremely close to us has passed on recently so that is good. We leave her with a sitter whenever possible.
At age 4, can she sit through an hour or two of speakers? Would it bother you to be her caretaker during those two hours (I've been to longer funeral services and that is a really really really long time)? Or do you feel that you need to be there to support your husband in his time of grief and mourning? At her age, she will likely not remember much about her great-grandfather, but may remember some things, the pivotal things, the important things.
I hope some of that is helpful. My daughter has a very good understanding of all this at an early age. I wanted that for her, because my father passed on when I was 19 and they never "met". And I want to help her as her views and mind form as she is growing up.
Any questions, just email me back!
V.