I'm so sorry... That is horrible to lose a father so young.
I would be honest but in kid terms.
My daughter is constantly asking about why my mom died, where she's at, why we buried her etc... I just answer away as the questions come in.
My mom died 2 years before my daughter was born so they never met but I have always made it a big deal to tell her she has a Grandma and she's in heaven watching over us. My daughter has had conversations with my mom (I know weird) and loves to go visit her grave which we can only due once a year or so becuase it's out of state. She get's very excited to pick out flowers. I think what helps with us is we talk about it alot. Look at pictures. My daughter is almost 6 and she doesn't quite get it all but she understands. She did for awhile think that a cemetary was heaven and I had to explain the difference.
You may want to do a few things:
As creepy as it sounds, My grandma took pictures at my mom's wake, yes casket, dead mom and all. I would stumble across the pictures every once in awhile and just break down but it's also helped me remember things from that day and I appreciate having them in a way.
Then we also called the funeral home and asked if just us children could go a hour or so ahead of the wake to say our goodbye's in complete privacy. My brothers and I were all teenagers and it was weird family circumstances(divorce,mom lost custody of us when we were little) so we did that and it was really good. Then we were able to join the rest of my mom's family later in the day already having had our "shock" moment. It was our 2nd funeral we had ever been to so it was a huge shock.
I think it's going to be harder on your daughter the older she gets and the more she understands. Just try and preserve memories make a scrap book of the funeral include the little program and stuff and talk talk talk........