Hissy Fits and 'Tude

Upon hearing the gender of our baby, I remember one friend (mother to two girls) telling me "Welcome to the world of attitude and hissy fits!". I'm afraid she was accurate in her assessment. Mya seems awfully young to sport the attitude she's been sporting lately. I'm not sure I'm ready for her 'tude.
As an example, we took Craig in to work yesterday and picked him up. The four of us were snug in our Echo back and forth to Huntsville. Mya spent the better part of all trips squealing, squirming, yelling and bellering. I have a sinking feeling about our upcoming road trip back and forth to Orlando in August.
When Mya hears the word "no", she lets out a blast. People look to me for explanation as though she just fell and caused herself severe injury. I have to explain she simply was told "no".
Today, she spent the majority of her day taking toys out of Lucas' hands. As soon as he released one and picked up the next one, she had her sights on that one too. By 5pm Lucas had had about all he could take of this and he started to hang onto his toys and push her around. Because he's the bigger of the two, he unfairly gets shut down quickly. Mya, because of her size and age, is getting away with murder.
Craig argues that with a girl this smart, we need to start putting limits on her because she certainly understands what she is doing. I have started to put her on the floor in her room, leave the door open, and walk out. She usually just joins me and recommences her tirade within closer earshot. I will keep you posted on what methods we come up with to successfully handle these fits. Something tells me you will be hearing more about this.