KnittingMama, pinip's very interesting points brought something to mind. You said that DS had similar issues in 1st and you pulled him out to homeschool. You also said that you told DD that 1st would be better. Maybe she's angry with you as well. Could it be that she sees you as having misled her about 1st being better? Is she angry that DS got to escape and she doesn't? Please understand I'm not trying to judge you or say that you really meant any of that, but might that be her perspective?
To be fair, 1st grade *is* much better than Kinder was. Her teacher is a million times better, and has been responsive when we asked for some differentiation. And DD loves her teacher this year (she merely "liked" her teacher last year). We've had many talks lately about all the things her teacher has done to improve the classroom, either for DD alone, or for the entire class. She knows it's better, so I don't think she's angry about that.
OTOH, I am also certain she feels neglected because DS gets to stay home, and I am certain some of her outbursts stem from the frustration of being DS's sister. The squeaky wheel gets the grease, and DS is very, very squeaky. What to do if you're DD? Become squeakier!