If your child has a cell button battery (i.e., watch battery) in her nose, go right to the emergency room. The chemical products in the battery could leak and cause serious burns.
Even if your child is well supervised, she can put all sorts of things in her nose like buttons, pebbles, pieces of foam, dry peas, and peanuts, for example.
If the object is sticking out of the nostril and can be easily grasped with your fingers, you can try to remove it. Otherwise don’t try to remove it because you could push it in further: take your child to the doctor immediately.