I don't think there's much difference between "people" salmon and "cat" salmon. (Most cats can eat salmon) If anything, people salmon is going to be higher quality. It's possible she might be allergic to salmon in general (has she reacted before?), or it's possible she ate something else that she found lying around. I had to stop mine from munching on a decomposing bird one night. She only goes out on a harness and lead, so if she was free roaming there wouldn't have been anything to stop her from finishing the revolting thing off - and probably puking it all over the house shortly afterwards.