I feel for your dd and you OP. I don't feel you've done anything wrong to create this situation at all.
Vaguely similar happened to my dd (and probably more to me!)
We're in the state school system. Our Primary was literally next door to the local Secondary. 99% of the pupils go there without any question. Many of the parents and their parents before them went to that school too (I don't come from the area and I found it all a bit weird). The thing with the school is, it's not a great school. Not awful, just not very inspiring.
When we came to choosing a secondary school, dd and I choose differently. A school only a few miles away but actually in a different LEA. A much better fit for dd. I never really mentioned our decision to anyone and just applied quietly.
On the day that places were allocated people assumed we were going to the same school as their dcs. When dd quietly said she was going elsewhere, I had parents cross the school yard to question me about my reasons and then to slag off any aspect of our chosen school they could find.
Then the texts and emails started. Texts from parents saying how 'sad they were for us' and how they'd heard from a friend of a friend of a friend of a cousins mums neighbour that there was a huge bullying problem at our chosen school. One mum (who I was friendly with) even said that it was a shame that we wouldn't be a part of the community anymore (I wasn't moving house).
There were lots of passive aggressive posts on FB about how "parents should support their local schools by sending their children there" etc. Comments about our decision even continued into Scouts after school.
At school the children continued to question dd and criticised our chosen school. Saying things they could have only heard from parents about Bullying, and drugs. Some pupils told her she was stupid to go to another school. She started being told that there was no point inviting her to things anymore.
The teachers would even talk down to dd about the school and often 'forgot' transition days for her and lost out transition paperwork twice.
The worst thing was, her entire Y6 class went on a week long transition period to the new school. The school didn't know what to do with dd.
Honestly, it was unbelievable. I've never experienced anything like it. The attitude of "if you're not with us, you're against us" was all prevailing. Dd was upset but tried to brush it off and learnt not to mention her new school at all.
Dd is now 14. After a rocky Y7 has made lots of new friends. I feel the decision to choose the other school was so right for her (and me).
I had to continue at the Primary school for another 2 years with DS. However I just didn't engage with any parents or even the school. DS is now in Y7 at the same school as DD. He loves it. Possibly a even better fit for him than dd.
Incidentally, all the old Primary school friendship group had broken up by Christmas at the other Secondary school and had made whole new friendship groups. I'm SO glad I didn't get sucked into the mantra that dd somehow had to go there because all her friends were.
Looking back it was an awful time, probably more for me has I had to field all the comments and passive aggression. The relief of finally leaving the school was huge.
I'd never noticed the 'crab bucket' mentality until we made a different choice. I'm so glad we made the move.
Sorry that was a long rant!
I'm sure things will go ok with your dd until the end of term. Just grit your teeth and get through it. Happier times are ahead for you both. Good luck.