Afraid of everything.

Question
I have a Treeing Walker Coonhound that was a stray. She has been with me for a year now, and with another family for 5 months before that. She is afraid of sounds, such as thunder, gunshots, and fireworks...along with car mufflers, the clanking of trash cans, the garbage truck 8 blocks away, planes that sound louder than normal, cicadas, etc. Any of these noises can shut her down immediately...mid-pee or poop, mid walk, the end...she shakes like a leaf and only wants to go home, or the nearest home, or nearest car...whatever is available. I have worked closely with her vet, who is also a behavior specialist. We tried medications, treats outside, treats on walks, but when the noises happen, that's it, she shuts down and no amount of training or treats will bring her back. Last night, after only going once a day for several days, she emptied her bladder in my living room. She had asked to go out several times, but would not go out the door (afraid).
During the winter, she was care free, running and playing, going out several times a day. Now, the birds and the bugs are out, sound is traveling better, and her quality of life is reduced to holding it all day, hiding in her crate, and refusing to go for walks. (I have a gentle leader for her, which does not stop her from pulling as hard as she can when she gets scared) I am concerned about her quality of life, and wondering if there is hope for her. I was even considering doggy earplugs? Any advice would be appreciated. I am very close to making a very tough decision for her, but I am still looking for hope.

Answer
What often works is just getting the dog used to things,slowly. What I have tried with several dogs was using a CD of nature sounds,and you can buy those pretty much anywhere and even only playing small portions of those throughout the dog will get the dog accustomed to noises. At first the dog might be skittish but over time even if they might not ever like some sounds will at least either ignore them or just go in a crate rather then urinating ect