I also see things very differently to most posters. I know what I am bout to say is going to be quite harsh, but I'm going to say it anyway!!
Ds1 went to a catholic feeder secondary, so 80% of his class went there. It is our nearest school. He walks or rides his bike. But apart from two old friends, I would say 20-30 of his friends are new. And they live further afield, so I spend quite a bit of time transporting him around, because these boys get the train to school. But the point is I had expected this. It was obvious. I knew the dynamics and transport needs from talking to previous pupils mums.
He has been mostly happy all the way through.
But that's boys. And I think they are quite different to girls. For girls friendships are very very important. and kinda more difficult to form, in the first place, I suspect.
So I feel like saying to the Op, with respect what did you expect?
Plus, she is clearly anxious. (which neither of my ds's particulary are).
So what made you send her to this school in the first place. Or what made you NOT expect this scenario? It sounds blatantly obvious to me. And could have been foreseen.
Did you not try and form friendships with some of the girls that you knew would be attending, in the summer prior to her starting year 7?
Or finding out which girls liked ....... ponies, flute..... certain boy bands/whatever?
Or approach HoY prior to day one?
Most girls struggle to form friendships. But if a dd is prone to anxiety, that surely this would be even more heightened?