It sounds like you've both been dealing with a lot. Children that age sometimes have trouble expressing their anger or unhappiness in any other way than acting up. But, if you let her get away with it now, she'll learn that whenever she doesn't get exactly what she wants, to throw a fit. When she throws a fit, tell her that mommy doesn't understand while she's screaming. And give her no other reaction.

I would talk to her ped. before seeking a therapist, I know that they're out there, but usually it's for extreme cases, children that have been abused etc. My friends son used to hold his breath when he'd get mad until he passed out. She was in a panic, what should she do, doc said let him do it. The more you reward the negative behavior with attention, the more negative behavior you'll get. Took a few months, but he did stop, he's currently 25 and working on a master's in psych.