She's learned bad behavior. At that age she's like a dog and you have to train her. It'll be tough and literally take the rest of her life. You can't expect someone that age to make a mature emotional decision. You as the adult have to decide if you're in for the long term commitment. If she ignores you. *** it. don't give her attention. eventually she'll give up. I can't imagine how hard it is to raise another persons child, but if you are going to do it, start thinking of it as your own child.
I have raised five children and only two were my own. And each of them had a different punishment that was unbearable to them. That the mere mention of STOPPED THEM IN THEIR TRACKS and immediately corrected the behavior. One was spanking, I spanked him
once in his whole life. he is nineteen and I can still say "you aren't too old for me to put you over my knee!" and he will stfu. One was the timeout corner. etc... Each kid has a different breaking point. Find it, then apply pressure.
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Once they LISTEN to you, then you can use positive reinforcement or ninja mind control or whatever.