Honey, it's a party. It's not the end of the world. A few days after the fact, you'll probaby have forgotten all about it anyway. I know it's difficult to understand, but parents don't forbid their children from hanging out with friends or going to parties unless they have actual reasoning behind it; they're not horrible, heartless monsters who do stuff like that just because they have the power to. Most of the time, anyway. Have you tried thinking about what her reasoning behind not letting you go could be, and tried to understand it and see things from her point of view?