How do I tell my mum…?

My mum and I have been talking about what college I should go to and she keeps recommending UCs, but I REALLY want to go to a state; specifically SDSU. When I bring it up, she shoots it down, but I know that's where I want to go. How should I tell her that it's my decision? Oh, and yes she will be helping pay for it but I will pay for a majority of it.