Thanks, all. MwM, it's my difficult child. I think we have the correct diagnosis. Whether or not the ODD/ADHD are the only things there remains to be seen. Her concerta does help, especially with her impulse control, but some days it doesn't seem enough. I'm sure it's partly my fault for not having a schedule to adhere to (our mealtimes and bedtime are the same each day, we just don't do the same thing the rest of the time, every day). Her misbehavior that bothers me the most is her near-constant fighting with her sisters. She pushes and pushes until they lash out or start crying. I end up with a headache every afternoon. Everything has to be her way, or she pitches a fit.
CrazyinVa, I've heard too, that if they say "I hate you" it means you're doing something right. Most days I can brush it off, but on days like today it wears me down. It doesn't help that the 5 yr old has started mimicking difficult child's backtalk.