Help!!!

We are having some um, 'behavior' issues at the moment. And they aren't the easy ones that can be managed with a three minute time out. My parenting philosophy has always been not to break her spirit, to respect her as a separate person and raise her to do unto others as you would have others do unto you. At this very moment I feel like that path is smacking me right in the face. I feel like a failure, like her independent nature, outspokeness and center-of-the-world-ness, as well as her inability to listen and follow directions are the direct result of me not being more stern and disciplined in the early days.

I am reluctant to call her a brat because she has a good heart and is capable of being kind, loving, and well-behaved but there are those moments, which seem to be lasting weeks on end, where she is intolerable. She is getting in trouble regularly at school. She cannot sit still or remain quiet, refusing to follow direction and she's hitting and kicking friends. She knows if she gets what amounts to a 'time out' at school she is punished at home. One time out equals no TV, two time outs and toys are taken away, three time outs and activities are cancelled. Today is a big day for her. If she comes home with another bad report we are canceling her horse riding lesson for next week. I really, really, really hate to do that because we are looking forward to it as much as she is, but something has to be done.

It's reached the point where I am thinking a professional needs to sit down and talk to her. Maybe they can find out if there's something deep down that is bothering her and causing this terrible behavior or if there's some magic trick for us to kick start her good-naturedness. I am at wits' end.