I'm going to make a rule where I'm allowed to be an asshole to my sibling whenever she starts to be an asshole to me
Is there a reason for this? What happened?
Because I've asked my sibling to stop being an asshole to me and she won't.
It can be frustrating when your sibling is being a jerk to you, but two wrongs don't make a right. When your sibling is being mean to you, you should retaliate by treating them with respect. It's difficult for someone to be mean to someone when they can't get a rise out of them.
So I should let my sister push me around all the time.
Just because someone is a jerk to you doesn't give you the right to do it back. You should set boundaries with her and tell her how you feel.