Melatonin. Its brilliant stuff and has helped my dogs no end. Its also worth trying a program of desensitisation, but its a bit late to begin this year. Basically you get a CD or download of firework noises and play it very very quietly at some distance from your dog while feeding her treats or playing her favourite game. She should not react to the noise at all if you have got the distance and volume right. VERY SLOWLY you increase the volume and decrease the distance and she should learn that the noises aren't scary. Unfortunately I have got one of the dogs for whom this won't work as he can tell the difference between real and recorded sound. He will sleep through a war film with his head on the tv stand but start to shake on hearing a firework that I can barely hear at all and may not have even noticed.
I am assuming you do all the usual things like making her a den close to you to hide in, playing music or the TV continually, taking her for the last walk of the day early and so on?