A very random thought, but have you had her eyes checked and does she appear to behave oddly in any other situations? My goldie has cataracts which is quiet common in goldies apparently, which means that she cant see very much when a light shines in the dark, which for my girl is very disorientating, so i try to avoid going out in the dark.
It probably has nothing to do with your situation, but it may be worth checking if there are any other problems, however it does sound like shes was scared by the firework. What is she like if you put your car headlights on in the drive when its dark?