To my knowledge (which is little, so i could be wrong) i don't think that the guidance counsellor will tell your parents anything without your consent unless she thinks you are a danger to yourself and/or others. If you're not a minor, she definitely can't say anything. Guidance counsellors talk to their students in confidence most of the time, as far as i'm aware, but before you say anything to her, why don't you just ask what the confidentiality policy is/will be? If you don't like that policy, then you can ask her to refer you to someone else like a social worker, doctor or therapist.

I'm glad you've decided to bring it up, it's an excellent first step on the way to recovering from all this. If you don't think you can say it out loud, why not write your guidance counsellor a letter and have her read it while you're in the office with her. Just tell her it's the best way you could get your thoughts across and that you're uncomfortable.