to the OP, i sympathize, i really do. what your mom is doing is completely disrespectful, and it's nothing i ever did, nothing i ever thought of doing. BUT, and i don't know what country you live in, or what state you live in, at 17, you are underage, and you cannot go against what your mom says (unless you can prove that she is abusive). you just have to suck it up until you turn 18 and move out. that's what the cop told my son when he and his dad got into it while i was gone for 20 minutes to pick up a freaking pizza (don't ask, it'll take a whole nother thread for THAT one!). you live in her house, you are underage, you have to abide by her rules, even if they are unreasonable.
having said that, once you turn 18, move out and can afford your own car, then mumsie needs to keep her hands off. in fact, she shouldn't even have a key to your car. and that lure of her helping you to buy a better car when you've graduated? check for strings attached.