That is a loaded question. If she did not know what was to take place she has a defense to the charge. Additionally, the State could charge her as an adult. The range of punishment could be probation to 15 years in prison, whichy is highly unlikley. Contact an attorney in your County as soon as you can.
I agree with the first answer and would add that for a juvenile it is important to assemble as much mitigation as possible as soon as possible and get that to the prosecutor. That means get report cards, awards, letters from teachers, coaches, employers, and / or anyone in a position to have a nice letterhead who knows her personally and can say something positive.
Such things can carry great weight with a prosecutor who is considering how to proceed in a case. If you can afford a private attorney familiar with the juvenile rules and laws, get one. They can get this material to the right people earlier than a public defender typically will, often before a decision has been made that is difficult to undo, such as a decision to file as an adult charge.
Juvenile sanctions are much less severe than adult sanctions - so the first and primary task is to make sure it remains in the juvenile system. Mitigation can accomplish that in close cases.
If remaining in the juvie system, then the punishment can range from diversion (community service and some other things in exchange for dropping the charges) to a commitment program, usually not lasting more than 6-9 months. Once it goes into the adult system, she is treated as an adult forevermore. Maximum punishments are much higher, her record would be as an adult, and the rules of procedure are less forgiving.
Get an attorney or get the mitigation to the public defender as soon as possible. Good luck.