That the girls responsible have been expelled shows that at least the school took it seriously, which is good. What have they said about how your daughter can return to school? What support will they put in place? Could she do mornings for a while to rebuild her confidence? Could you ask that she is moved to a class with none of their relatives?
is the school part of a trust? What about other schools in the same trust? I suspect you’ll have to go in and insist, refuse to go away, make lots of noise and be a very pushy parent to get this sorted. You shouldn’t have to but school are terribly short of resource at the moment.
or could she go to school from your mum’s house? Or your ex’s house? Would that put her in a completely different area? ,