My 3 year old BOSS....please help me!?

At 3 years old, she is defintiely old enough to understand consequences. If she is misbehaving, give her a warning. Tell her 'if you continue to XXX, you will sit in timeout'. If she continues, pick her up and sit her in timeout. Make her sit there for 3 minutes. If she gets up, pick her up and put her back. Don't talk to her or make eye contact while she's in timeout or when you're putting her back if she has gotten up. When her time is up, tell her what she was doing wrong, why that behavior is unacceptable, and make her say she's sorry and hug you. If you're out in public, give her a warning and tell her if she continues to misbehave, she will lose her favorite toy for the rest of the day (or week). If she continues, you *have* to follow through. Always be calm, crouch down to her level and look in her eyes when you're talking to her. Be firm and calm. Being consistant is the most important thing. If you tell her she's going to have a consequence, you *have* to follow through with that consequence. After a few weeks of this, I bet her behavior is much more acceptable!