Disciplining S

S has over the last few months started throwing a lot of tantrums and generally misbehaving when she doesn't get her way. I initially put it down to the fact that between December and January we shifted houses, changed her school and her baby maid stopped coming (she had been with us for a year and S was quite atatched to her). But for the last 2 months she has had her Ajji and me at her beck and call, and she is entertained every minute of the day. So i thought the tanrtums would die down without me needing to resort to any disciplinary steps, but that is not to be. Nowadays she screams if me or my mom have lunch instead of putting her to bed, or if we try to brush or her hair, and her recent peeve is that i should not feed the baby, or i should not burp the baby and i should instead put her down on the cot. Today i got really upset when S called me stupid for refucsing to stop burping the baby. And i am really at a loss on how to handle this. I tried to get S to apologise for calling me stupid but she is being very stubborn and refusing to say sorry. I dont want to give her timeout for this, i think when she says mean things she should say sorry, but however many times i have asked her to say sorry she just refuses to. I have refused to speak to her, play with her and even carry her, and she seems to understand that this is due to her bad behaviour and while that makes her upset, she still refuses to say sorry. I don't want to press the point any further (its already been an hour of the cold shoulder and its not having the impact i wanted) but I feel that if i dont make her apologise she would think she can get away with it. So what do you think, continue the cold shoulder for some time, or give her a timeout (consists of being alone in a room for 2 mins), or just forget it.