This is a fairly common condition in some lines of GSD's (believed to be hereditary) and I bred a bitch puppy who had it. I was told to give her soft liquified food to help it go down, but found that this made her bring it up again, and I eventually got her settled on complete dry food, finding the biggest nuggets I could so she had to chew and swallow each one individually rather than gulp the lot down.
Sadly although I rehomed her to what i though was a good knowledgeable home, able to cope with her disability, their vet said there was no point in carrying on and they had her put down without even telling me. I was so angry that I had gone to the trouble of stabilising her, and would certainly have had her back if they had let me know.
I have got an article somewhere, I will try to find it and post the link.
Bit worried about the salmon, (got an article on that somewhere too!) but hope you keep your girl stabilised.
Keep us informed.