Try putting her on the lead and get a friend to ring your door bell, then give her a treat. Do this several times and maybe ask friends if you can do the same in their house, so she gets used to a nice experience with door bells that sound different. Also take her to the vets without having any treatment, sit in the waiting room and give her treats, and if possible get the vet to make a fuss of her. Okay it might cost you a consultation fee (but if you explain I am sure the vet nurses would be willing to make a fuss of her during quiet times). I show my dogs and they have to go on a table to be examined in the show ring. When they go to the vets I never put them on the table, in case they associate this with showing.
I have a similar problem, although not fear, when a doorbell rings on the telly my lot go ballistic as they try to con me there is someone at the door. Is it me or are there lots more doorbells on telly lately? One of them also does it if he hears a dogtag on a dog's collar on telly, such as Monica the greyhound on Corrie, and also Bullseye on Oliver Twist (although I think he heard him panting!). As I am typing this someone is recycling a Christmas tree and they are barking at the jingling of the ornaments they are taking down!