Is her weight good? How much are you giving her in terms of treats and stuff? If she gets a lot of treats, maybe she is just not hungry for her meal. That was what I was doing wrong with my GSD mix, she was getting too many extra special yummy treats (peanut butter!! bacon!!!) that when dinnertime rolled around she was like, "Meh."
Bt then again if as you say she is passing on her dinner to the point of being sick on an empty stomach, then maybe Diane is onto something and she does not like the food you are giving her. I always add homemade chicken stock to the kibble I feed, and my dogs seem to enjoy that.
Leah: Newbie dog owner
Niko: American Showline GSD 3 1/2 years old
Rosa: American Muppet Dog (GSD/Border Collie mix) 4 years old