I want my girlfriend to stop being friends with her best friend
Why would you want your girlfriend to give up her friend?
I don't like my girlfriend's best friend
If you don't like her you should ignore it or break up. You should not try to control your partner it is unhealthy.
I'm going to get rid of her by breaking my girlfriend's spirit.
That is incredibly cruel. You should talk to your girlfriend about her friend and limit your time around her.