My 4 months old shih tzu puppy wont eat packed wet or dry dog food, plz help!?

my 4 months old shih tzu puppy wont eat packed wet or dry dog food. she gets 3 meals per day and no snacks in between to munch over. she gets treats while training but thats not enough for her to skip meals. she is very playful & active but looks skinny & weights around 6.6 lbs. what should i do to get her to eat?