Why did you do it, if you did? Do you now regret your actions or just don't care like so many other young people?
If you have no previous convictions, you might get off with community service, maybe a suspended sentence or you could go down for a couple of years. Have you not asked your solicitor, what is the probable sentence?
As she is under 18, velvetee, different rules apply.
Prison sentences (whether immediate or suspended) cannot be given to those under 18 for these offences alone, and the likely outcome, provided you are not a "Persistant Young Offender" is a "Referral Order".