Yea I do think she had a valid complaint. Why the hell didn't they refund her?
I know it didn't make any sense. Maybe it was a discrimination thing but they managed to keep it out of the media and avoid the turmoil. It's the only explanation that makes sense of why they weren't refunding her cash when they couldn't give her the meal she had ordered.
I don't care about McNuggets, they're not so good I gotta get 'em or anything, but the principle is what matters here. She ordered some nuggets, paid for them, they realize they have no nuggets, she should get her cash back. In any restaurant where the you pay afterwards it wouldn't have been an issue as no money would have been given if the nuggets didn't arrive.