Is it biting or is it playing?

[Pilot]

my new female cockatiel that I just got yesterday has started to nip just a little bit. She is hand fed and only about 3 half months. Is she biting aggressively or is it just play/grooming type bite. It is not hard at all almost like she is just putting her beak on me and that is about it. And if it is biting how can I stop it? I am telling her no in a firm voice, but do I tap her beak lightly? What do I do? I don't want it to turn into a problem so I want to stop it now rather than later. Also I don't want to discipline her in the wrong way either. Any suggestions would be greatly appreciated.