My puppy isn't eating her Merrick food but is still playful. Why?

Thanks for using Petco Pet Education Center, formerly Petcoach! What you are seeing may be normal, or it may be indicative of an underlying issue, it is difficult to know for sure. There are some dogs who are good at self-regulating their food intake; when they are full, they stop eating and then come back again when they are hungry. It could be that her growth spurts have slowed down and she doesn't need to eat as much as she did when she was growing so rapidly. It can also indicate an underlying GI upset, however (intestinal parasites, foreign material ingestion, gastritis, etc.). If she is acting normally, good energy level, normal stool, and no vomiting, then I would continue to monitor it over the next couple days. If she starts not wanting to eat, vomiting, have loose stools/diarrhea or otherwise acting ill, then I would recommend she be evaluated by a veterinarian to determine what the underlying cause may be. Good luck!