None of my ponies even blink at fireworks going off. Pride will even stand and watch them.
Even Reeco who I was very worried about this fireworks night (first time he has been in a place where fireworks were very close) was absolutly fine with it.
TBH sitting in the stable with horses tends to wind them up and make them think something is going to eat them (because they pick up on your worry). Close the top door of the stable, leave the light on and a camera up and let her realise that the big bangs don't actualy hurt her! Yes she may stress for the first hour or so but she will get used to it and settle down