My 6 year old daughter tells me her brain is telling her to be mean

My 6 year old daughter tells me that her brain is telling her to be mean.  She is usually a very good child and she does very well at school.  She does have problems with her speech and is in speech therapy at school and at a local univeristy.  I have been told she shows signs of auditory processing disorder and I have also been told that she isn't old enough to be tested.  She has problems with discipline but only at home.  I know most people are going to say that is normal, which I would agree to a point.  She screams and throws things.  I'm really worried that she is going to hurt herself or her sister.  There are times I have to hold her down and talk very softly in her ear to get her to calm down.  When I ask her what is wrong, she tells me her brain told her to not listen or to be mean. So has anyone else dealt with something like this?

[margypops]

It seems that the problem is at home not school what is it that triggers the tantrums, is her sister younger than her, are there any jealousy issues ?