Fireworks and Toddlers

I was convinced last year would be the 4th of July... the one where we have a fun cookout and all enjoy the fireworks. It was the first time in years neither Hubby nor I had to work. I prepared the girls by explaining that fireworks are loud but oh so pretty.
The night started out nice. We had a cookout at my in-laws and then we all headed to a lake in their neighborhood to see the show. After the first "boom," all the girls jumped in someone's lap, but they seemed to take it all in stride... all the girls, that is, except for Sue-Sue. She wanted nothing to do with it. She screamed. She cried. She practically tried to climb on my head. I made the decision to walk her back to my in-laws and sit in the car until everyone else was done seeing the fireworks.
Once we were in the car I asked Sue-Sue what was wrong. "It's dark out. We aren't supposed to be outside when it's this dark." Made some sense to me. She and I could see some of the fireworks from the car and she actually enjoyed them that way... but mention leaving the car and she wasn't having it. To this day I'm convinced it's the dark and not the loud noises that bothered her. (She is not typically scared of the dark, but it was the first time she had been outside in the dark).
I won't have a chance to test my theory this year. We have a friend who is a "4th baby" and her birthday party is the next morning. Rather than risk taking four grumpy girls to the party we're skipping the fireworks so we have four happy girls ready to stuff themselves with birthday cake.