All I can say is don't worry
I know easier said than done, but my daughter settled fantastically well in exactly the same position a couple of years ago - most certainly no regrets
The school do have an induction day where she will meet her new class mates and form teacher. There will be plenty of other girls in a similar situation, you may get the opportunity to ask if she can be placed in a class with girls in a similar situation, we decided not to place any requests. Though sad they leave there current friends, we found that even the old cohort from primary all changed friends in secondary.
Well done - SHE WILL LOVE IT !