First of all, congratulations on adopting Sophie. Rescues are the best, aren't they? Neither of our current dogs are afraid of thunder, but we once had a big tough athletic German Short Haired Pointer who was terrified. He would hide in the bathtub and not come out for hours. My pugle, who is now 50 lbs and tough as nails, used to be afraid of the stone lions in front of some of the houses around here. Plastic bags blowing in the wind, sprinklers, and pop up halloween decorations were also terrifying. Now, nothing bothers him. Daisy, my rescued chihuahua terrier is terrified of the ironing board, large boxes, and the vacuum cleaner. She even starts barking if I pick up the iron and she is on another floor. How she hears it I don't know. Who knows what happened to poor Sophie in her life. You just have to love them and pet them and make them feel safe and calm.