You need to slow, slow down.

You are in high school. THIS WILL PASS AND WILL NOT LAST FOREVER.

Pretty much every single thing I can think of is better than murder and suicide. Even running away and sleeping on a park bench. Forget the car. I know you don't think that you can survive without it but this is a whole new ball game here.

The first thing I would do is go to the school counselor, and let them know what's going on. Beg the counselor for the police or someone to intercede before this gets worse, and TELL HER you need EMERGENCY PSYCHIATRIC HELP (in fact, I seriously think you need to go to the hospital; I volunteer with suicidal youth and I think that's the best place for you right now. There's no shame in asking for extra help, and they'll give you the tools you need to survive Nmom if she tries to make life a living hell once you get out of there).

Let's face it, even if she finds out that you told and makes your life a living hell, even if she hurts you... it's not you going to prison. Prison means you can't leave and there's no way out, EVER. Even IF you get away with it, that's you living with her blood on your hands for the REST OF YOUR LIFE, and if you kill yourself to escape it, that's you throwing your life away FOR HER. She doesn't deserve that.

It doesn't matter that you're not good enough for her. You could be perfect in every way and it still wouldn't be good enough.