Thank you for the update.
A one day suspension is inadequate, as I'm sure you already know. I'm glad that you've contacted the police.
The school needs to put in a place a risk assessment for each individual culprit. I'm not sure how things are managed in England (where I assume you are) but in my LA in Scotland permanent exclusions are not allowed. However, it is possible for there to be a whole-school transfer. Whether it's done via whole-school transfer is expulsion is immaterial.
It is going to be difficult to manage because of the number of villains (sic) involved. However, that is not your problem. You might find senior management proposing a change of school for your daughter - because it's easier to move one pupil rather than several. However, there is no reason why your daughter should be punished by a move to another school because of the other pupils' criminal behaviour. Moreover, you have now established that your daughter is not the bullies' only victim.
The fact that the police are now aware strengthens your case.
You say that you "heard" that there had been a one day suspension. I'm wondering whether you were informed officially or via another parent? If you've had no feedback at all from the school as yet, make sure to add that to any letter that you send to officialdom.
As a bare minimum, the school needs to ensure that your daughter has no contact with these reprobates on school premises. You're going to have to be assertive.
From experience, schools often deal with bullying by allowing the victim to leave class/school early in order to avoid the bullies. In my view, this is simply allowing the bullies to win and punishing the victim by depriving them of part of their education.
I'm just mentioning this so that you can prepare yourself for such "helpful" suggestions from the school.