Call police asap and report this assault and make it clear it is not ‘a school matter’ but a police matter and needs thorough investigation.
Letter to school stating factually what happened (what when where etc) the background bullying and how you are still awaiting a response from the school and this inaction is totally unacceptable.
That child will not be returning to school until you have written confirmation of how this is being dealt with and what’s steps are being put in place to deal with bullying and to ensure this doesn’t happen again . State that you have reported to police .
ask what supportive measures they are putting in place / counselling / mentoring etc to help her get over this.
this letter would be sent to school head and then I would CC in EVERYONE that I could think of :
governing body, individual letter to named safeguarding lead at school, head of pastoral support, form tutor, head of year etc, head of safeguarding at local authority, local MP, educational welfare officer at La., Social services , director of children’s services
(just look them all up on council / school website)
in short you go nuclear.
politely and factually - no need to be rude -
but you ensure that with anyone with interest in child welfare knows what these despicable children have done and also how displeased you are in how appallingly this has been handled.
you are not ‘making a fuss’ - this is serious and your child needs you to step up and ensure it never happens to them again.
you have right on your side . Do not let this go.