I didn't experience a death close to me until I was in high school and I was a wreck. It has taken me years to not find reasons to avoid memorials and funerals. I knew that I would do it differently with my child. Not criticizing my parents, of course, they thought they were doing what was best.
At three, my daughter has been to three viewings/memorial services...and, yes, she has seen the deceased. None of the three were particularly close to her, but certainly people that she recognized.
At four, your daughter certainly has more awareness than my daughter did at 2.5 (the last funeral), but I am a full believer in exposing children to the realities of life.
We've also lost two pets...and my daughter was much more affected by that since they were a daily presence in their lives.
I plan on checking out the Sesame Street program that another poster mentioned.