Ridiculous... no... ludicrous!
As you know, Nedjeda, people who "think" they know about diabetes actually do not. Even the nurse you deal with probably thinks she's managing something very unique "for you," but in reality, they don't know it until they've lived with it (or a family member with Type 1). If they know someone with Type 2, they've still got it all wrong, and yet think they know it all.
I'm assuming you live in the USA. If so, you can get a 504 plan. You'll have this all resolved. A good tactic on getting them to do what you want is to make them think they're helping you (human nature is that people like to help).
Here's where you can go to get a rough template for your 504 plan:
http://www.childrenwithdiabetes.com/504/
The school must accept it if they receive federal funding. If not, contact the ADA by finding their phone number for your area (
www.diabetes.org). They will appoint a lawyer for you to resolve your situation, to allow you to help the people who do not yet know how much they want to help you. The ADA may even appoint someone to meet with the school, and the volunteer lawyers in your area will get you the funding you need for college should they refuse your right to carry medical equipment with you.
The "line cutters", unfortunately, if they have not grown up by this stage in high school, they will never grow up. Don't waste too much time feeling sorry for them or else it will frustrate you when you think about the unemployment benefits you pay them ten years from now.
Check into the Multiclix lancet device (from Accuchek) -- it has no sharp parts to it, and showing them a device like this might help allow you to carry your test kit around.
As far as the principal's excuse about that past diabetic, he/she needs to get over it and move on.