Lol, you have one smart dog. Actually, lots of pet owners go throught this. Cats do it too believe it or not. Basically your dog has figured out that he/she has a choice in what to eat. “If I dont eat my food, Mommy gives me something tastier.” To deal with this you can either cater to the habit or break it.
First, there will be no brand of dog food that you can buy that will hold his/her interest for long. To cater to it you basically have buy a healthy dry food to act as a base or food staple, just like how different cultures use rice or pasta as staples. Then buy an assortment of toppings; meat rolls, ground beef, cheeses, or gravy. So you use the same dry dog food and you add a topping on top, switching it up occasionally.
To break the habit (and this may sound hurtful but its not), you have to stop giving her tasty toppings or switching her food. Your shepard may not eat for a day or day and a half but thats ok. Just keep the food out, replace it with fresh dry food even. Eventually your dog will learn that the hunger strike for tasty topping is no longer effective and begin to eat. I’ve seen this so many times at my job, vet tech, and even gone through this myself. Last year my siberian husky had surgery and she stopped eating because she was painful. So to entice her to eat to promote healing, we began giving her toppings like cheese and chicken. Once she was better she continued this habit, refuse to eat to get tastier meals. Eventually, i called her out on her food strike and gave her just dry food. She resisted for a day but gave in. No more bad habit, and I save money.