I'm thinking of running my girlfriend off by throwing things at her
Are you really planning that? Isn't that pretty violent?
She is a stupid bitch, always spending money on things she doesn't need.
Your girlfriend likes to buy too much which makes you angry, that's easy to see. You will be apprehended for abuse if you chose to do that, there's an easier solution. Break up with her so things won't resort to violence.
Break up with her and then beat her?
No, I am not suggesting to beat her up, that can land you in jail. If you really dislike her, I think it's best to just break up and stay away and get on with your life. How would she feel if she always had to worry that you'd hurt her?