I think you’ll have more success here if you wait and see how it is in September and then go down the complaint route if they do not deal with the bullying.
From a safeguarding perspective they can’t (although many do) just ignore it and if it’s an ongoing issue it may eventually be an easier choice for them to move one of them to another class.
To use your work example, my team gets mixed up every time we finish a project and I hate it. I miss the people and there’s been one or two teams where we really worked well together and I got moved to a worse team. However I cannot expect them not to do it. It is normal as adults to be mixed up from peers.
You’re right I wouldn’t expect to just carry on if I was bullying but right now - as far as the school is concerned - there’s not yet been any bullying there. The bullying was outside school, some time ago and they weren’t informed. Right now they’re not expecting her to put up with bullying. If in September the bullying starts then your point is perfectly valid.
In the meantime I would teach her and practice scripts on how to respond to things in a way that is firm, will get an adults attention and leave no room for blaming her.
eg other child calls her a name teach her to say firmly “do not call me that” instead of ignoring it or calling names back. In the case of any sort of pushing / hitting etc then a strong “don’t hurt me” followed by immediately moving to safety and telling an adult very clearly eg “Jane just kicked me in the leg”. Lead with a statement of what happened and not the story leading up to it. Practice with her. Roleplay and practice projecting her voice. Talk through situations she’s worried about and roleplay what to do.
In September record everything. Report everything factually. Exactly what happened and when. Include the impact on her life and mental health eg today she said “nobody likes me” or this morning she cried before school and said “I don’t want to go because I’m scared”.
Don’t assume every new adult who joins the school will know about this even if they should. Try your very best not to end up in a situation where it can be claimed that they’re both doing it to each other.
As a teacher I very often ended up in a situation where two sets of parents insisting their child was being bullied by the other. This had been going on for years and years and every time I tried to get to the bottom of it it would be “x did this” “yes but because y did this”. Often this was late primary going all the way to back to issues from reception class. Both parents insisted their child was the one being bullied and whenever their child was caught doing something they insisted their child understandably snapped after dealing with bullying for so long. SLT was extremely unhelpful and this was very difficult as a teacher to untangle.
I know she’s not a robot and it’s not easy not to react but it will help if you can make sure that all the evidence shows this is one sided. Witnesses - other children - tend to be very honest at this age about what they saw happen.
Remind them of their safeguarding responsibility.
Look online for official guidance on what they should do to keep her safe. Don’t use chat gpt. If you use it just use it to help search and then visit the actual websites and quote the relevant parts directly.
Point out clear but concise evidence regarding the affects of bullying if needed and expectations of schools. Anything official from gov uk / NHS / MIND etc would help.
Be persistent, calm and fact-based. Escalate to the correct channels. Force them to write down specifics of whatever plan they are putting in place and find out when it is being reviewed for effectiveness. Show them you will not relent and will not allow your child to suffer.
Or move schools. That’s understandable too.