I can't imagine being in your shoes but it sounded to me a lot like a personality thing too, but they can't diagnose a personality issue until the day after a kid turns 18. Which in my opinion is too late. Someone here suggested DBT I think that would be a good way to go. Maybe you can talk to your therapist about ways you can incorporate DBT into your interactions with her. I'm not sure how well it works for an oppositional disorder tho. The individualized plan for behavior and school sounds good too.

I don't know if my daughter had BP in high school( there's a good chance she did) she was using drugs (self medicating?) and voluntarily went to an alternative school for 9th and half of 10th grade were she caught up and graduated with her friends. She loved it because it was easier to concentrate and have an individualized plans for her classes. The school she went to had no talking during class times and everyone worked on different subjects at their own pace. she said the quite no distractions atmosphere helped her a lot the only thing she missed was art classes.