Please take her to a good vet. Ensure she is dewormed. Make sure you are giving her a balanced diet. Some of the commercially available puppy food are quite good (royal canin or hills science plan). Also ensure she is getting sufficient exercises.
If your vet confirms that your puppy does not have a health issue, then your puppy should be fine. Just like humans, not all dogs are the same. Some are lean and muscular while some are chubby. So don't worry and just keep feeding her well, exercising her and making regular visits to the vet. Your puppy will be fine :)