More Precocious By The Day...

Callen got in trouble at school today. Evidently she was taking toys away from some of the other kids and her teacher Ms. Emily asked her to stop taking the other kids' toys. Callen's reply was "No." According to her teachers this is the first time Callen has talked back to them. She was put in time out to think about her actions. She's been talking back more lately at home too. Any suggestions for how to 'nip this in the bud'?