To be sure that no one on your doctor’s staff gives out information that you do not want known, your best best is to put it in writing, sign it and take it to your doctor’s office. While there make sure you tell them what information you do not want your Mother to know so that they can tell other staff members in case you Mother should call in.
But all of this is pretty much a moot point if you are a minor.
If you want your Mother removed from the list of people to be notified of your health information, you really need to put it in writing. Make sure you keep a copy for your own records in case there are any legal repercussions to deal with later on.
When the HIPAA laws were first instituted a few years ago, doctor’s staffs were afraid to even have a sign in sheet at the front desk so a person’s name was revealed, but now things have gotten lax again, and the guidelines are being broken on a daily basis in many offices, so you do need to be careful.