They kind of let her pitch a fit until she's done. They've tried everything else, and finding that nothing works, they just let her go until she's done. Once she calms down, they let her have a little time to herself, and then she'll act like nothing happened. Although, sometimes she does seem to be remorseful. She felt bad and apologized a few days after kicking the nurse at our doctor's office.
She also doesn't seem to need sleep, and most nights I don't think she actually goes to sleep until midnight. One night she woke up and watched a movie in the middle of the night.
Her first day of preschool was awful. My niece cursed out the teacher and was throwing chairs anytime any of the kids tried to come near her. She's gotten much better, but they ended up taking her out anyways, b/c she's still not doing "well" with preschool.
What's really tough, is everyone around my niece is trying not to set her off. I know I decided one day I was going to brush her hair whether she fought me on it or not. boy did I feel like an idiot when she spent the next hour screaming. A normal kid you can just tell that you are going to brush her hair, and she may not like it, but she'll get over it after a few minutes. My niece is not normal. Now I kind of back off, and let her parents handle her. I think that's the hardest thing for outsiders to understand- you can't treat her like a normal kid.
I think we're at the same stage in the game as you are, still looking to get a diagnosis so we can learn how to treat the issue. We were really thinking autism until about a week ago when someone suggested bipolar. Whatever it is, it will be a relief to get a diagnosis.