I would expect them to give her this intra muscularly as you arn't supposed to drink or eat anything before surgery.  I note that any procedures that either my kids or I have had done, they tend to leave explanation of what is going to happen the day of the op or the night before if your admitted then.  However, in your situation in having a child who needs surgery and him/her having CAH I would fully want to know exactly what will be done right down to the last detail (including the dose of the cortef and when and how this will be given) way in advance.  If only to save worrying about these sorts of things you would think that medical proffesionals would think about the parents.  It is only normal to be anxious before your child has surgery and that I say from experience having had my son have just a short minor op and he has NO CAH.  My son with CAH has never had anything done in that sense but if he did, I'd be asking questions and wanting answers even if it were only to be able to console myself that the people answering them KNEW what they were doing and were concerned enough to explain so much---to make me feel a little more relaxed.  How far away is your childs surgery?  If it is relatively close you have a right to know what will happen in depth.  You should not have to be worried about things at all---if it were me I would be wanting answers before I left---but I know that sometimes we may not ask these things incase we are perceived as being overly concerned or anxious. You have a right to be and don't be worried about asking next time there is an opportunity.  If you don't see your childs consultant until the day of the op then ring and chat to them and just tell them you feel a little anxious. 

JH