edited to add - T., you can add to your original question (don't delete anything - just write at the bottom ETA (edited to add) OR put it in the So What Happened, like you already did. It's the only way to respond here on this thread (it's not like facebook). You did it right...
Original:
If I were you, I'd get an appointment with the school district's child psychologist. Every district has one - he or she works out of the main admin office rather than in one of the schools. Ask if there is an elementary school in the system who has special classes for children with problems. There usually is one.
Most parents don't want their kids in a program for troubled children. BUT, if the school is sending her home every day, then something has to be done. She can't learn if she isn't in school. The teachers who deal with specialized classes are specially trained to deal with these kids, and they are typically brought in from area schools after being identified as children who cannot cope in a traditional setting.
This doesn't mean that your child is retarded or mentally impaired. Hopefully your district doesn't put these children and behavioral problems together. Talk to the district psychologist and ask questions - listen to what she says.
I'm sure that one thing that they would want to do is have her evaluated. Has the person she's working with done an evaluation? Do you have a copy? Have you given it to the school counselor? The school can do their own evaluation (you don't have to pay for it.) Write a letter to the school asking for a formal evaluation, mail it certified, and they have a certain amount of time (maybe 10 days?) to answer you and set up a date for evaluation.
Keep on this, both with the school and with her therapist. I agree with the principal to keep sending her to school. She mustn't think that bad behavior makes it so that she doesn't have to go. I do think that getting her transferred to a place that deals with students like her will help her learn that she doesn't get to go home in the middle of the day. When she learns to behave better, whether it's with medication or behavior modification (or both), getting to go back to regular school where there is more "freedom" will be a reward for good behavior. Right now, she has nothing to compare to and doesn't understand.
Good luck.