Welcome to the board. I'm glad you found us.
ODD is rarely a stand-alone diagnosis (diagnosis). It is more a basket of symptoms caused by an underlying disorder (such as ADHD, bipolar, etc) and once that underlying disorder is treated the ODD symptoms dissipate. I would believe your daughter when she says she can't help it. I haven't met a kid yet who just wants to be bad for the sake of being bad. Kids, especially at her age, want to please their parents.
A book highly recommended here is The Explosive Child by Ross Greene. I think you will find it very helpful.
I'm not the first one to jump on the medication bandwagon. It was a long time before I would put my difficult child on medications because noone gave me a firm diagnosis and I didn't want to just medicate symptoms. However, some disorders are biological in nature and some of these kids need medications just like a diabetic needs insulin. And the difference in difficult child with her medications is HUGE. I actually see joy in her face now. I never did before. I encourage you to keep an open mind about that when you meet with the professionals. by the way, a psychologist is not an MD and cannot prescribe medications. A psychiatrist can prescribe medications.
It is important for you to take time for yourself and time for just you and husband. As others told me when I first joined, this is a marathon not a sprint.
Again, welcome.