The System is very transparent about what people eat. The last thing it needs is a scandal. Most just never meet the Animal they're eating unless it's an intimate gathering where the Animal is usually family or a close friend.

Riley was more reacting to the fact that, even though it was very brief, she had met Rosey. But she knew enough about Livestock now that this wasn't sad for them. It was completion.

Not eating would have been disrespectful.