Need help with problem almost 13 year old girl

I havent spoken to her therapist directly, but that is something IҒve been considering trying to take a bigger role in. My aunt has so many doctors appointment of her own that its a way I can help out. The therapist has suggested before some rather basic things like house rules and rewards systems but hasnҒt been helpful on what to do when those dont work. ItҒs all well and good to say that she needs to write a letter of apology or do chores to pay for things she has stole, but what do you do when she completely ignores you, wont do it? WeҒre locked into a power struggle with her where as soon as you take something away, she doesnt want it. If you try to talk to her and sheҒs pissed off and doesnt want to listen, she has no problem just walking out the front door. SheҒs been diagnosed so far with just depression and anxiety and her therapist is helping her with specific issues related to her mom. He hasnt been seeing her long enough to diagnose anything more serious. She isn't on any medication yet, but that is being considered if just talk therapy doesn't help. Her grandma has very little confidence in the therapist, but heҒs the only one close thats covered by insurance. He doesnҒt have experience dealing with kids with this many problems and far too many other patients.