In the experience and the beliefs of many parents here, ODD is not a stand alone diagnosis. It appears in almost all childhood disorders--autistic spectrum disorder, early onset bipolar, mood disorders not otherwise specified, and others. The best treatment is to find out the "bigger" diagnosis. that is causing it and treating that. I think probably all our kids have ODD, but there are other factors involved as well. Depending on what is causing the ODD, the child may or may not know what he is doing, but, no matter what the cause, extreme defiance is a big red flag the child is has either a psychiatric or neurological disorder. Kids don't wake up one day and think, "Wow. Great day to make my parents nuts." They are kids who are very unhappy and you kind of just need to keep digging until you get the whole picture. It is extremely rare to get the whole, correct diagnosis the first time you go for an evaluation. I love neuropsychologist evaluations because they do intensive testing. There are no mothers here who can answer your questions and know for sure that we are giving you the right answers. ODD behavior is caused by so many factors...
Until you figure out the big picture, I'd buy "The Explosive Child" and use it. Since bipolar is on the family tree, and is hereditary, you may want to read up on it. There is a great book called "The Bipolar Child" by Dimitri and Janice Papalous, and here is a link to a particular website the describes it. Your daughter saying that something in her head is making her do it, could be auditory hallucinations or she may just be so out of control that she doesn't have a clue why she behaves like she does. I"m not saying your child has early onset bipolar, but it is definitely something you need to keep an eye on since it's in the family.