Is it possible that she's rebelling because she - in her mind - got ripped away from friends? Maybe she's also overwhelmed?
I would say you definitely have the trigger point in mind then. Who knows what else is going on in the new school that you as a parent don't get to know easily?
I can only think how I'd go over it with my daughter, so this might not work for you. I would leave the matter of the meds to the side for any discussion for a little bit. Figure out the rest of her circumstances first, then reintroduce the meds once she feels understood again. This can also be very soon. Just don't make the talks about the meds for now. Again, I don't have experience with PDA but if you push too much too often it can be counterproductive even before factoring that in.
You will most likely have to get a new prescription for the strattera as well, as going from zero back to full will be problematic. It needs ramping up time with the dosage. Otherwise there will be side effects that might lead to setbacks. That's personal experience.
You got this! Best wishes to you and your family.