I've had a few picky dogs under 10lbs and under 5lbs. I find many times they aren't a fan of the kibble or food. 3lbs for that age seems normal though so don't freak out yet. Especially soon after you bring a dog into your home you will need to learn their tastes. My recommendation? try mixing her kibbles with some dog friendly veggies, try some dog friendly fruits. I've also had a dog that really enjoyed kibbles mixed with a crushed dried liver snack.