Thank you for contacting Just Answer. I am very sorry to hear about what has happened. I commend you for making the appointment with the child protection officer at your son's school. When you go there you must ask them what can be done with protective services vis a vis your daughter. If they do not intervene, then on your part, you need to punish your daughter for her behaviour. I would send her to school but not allow her to have ANY privileges for a month. No saocializing with friends, no TV, nothing that she wants to do. She needs to learn that her behaviour will absolutely not be tolerated under any circumstances. Also, I would say to her that if her brother did something to her that she did not like and felt that she could not handle it then she needed to come to you for your assistance. It is not tolerable to physically attack her brother. So for one month I would institute the punishment.
I see that you are offline now. Let's chat some more when you get back online. If I am not there when you return, just add what you want and then I will respond when I get back online. She has to suffer the consequences of this behaviour. Just apologizing is not sufficient. Yes, an apology is necessary but it requires more. What she did is totally egregious.
BTW, whether the Protective Services intervene or not you still need to punish her.
I want to add that I am not one who would give such dire punishments but for doing what she did to her brother she must suffer the consequences.