I don't want my cousin in my house.
Why wouldn't you want your cousin there?
She caused an accident before.
I don't know what kind of accident she caused, but if it was something minor, you should still let her in. If it was a major accident that involved injury or death, I understand not wanting to let her in your home.
I'm just a cold hearted bitch.
It sounds to me like you are not wanting her in your home more for selfish reasons. She is family, you should be able to forgive her for whatever she did. It's normal to let family into your home so you can have a good relationship with them.