Dear Jenna
Gosh. I feel your pain about your granddaughter ignoring you. The thing is, this girl is over her head. She can't handle the conflicting loyalties to which she is exposed. No child this age, could. This is the time when you need to be extraordinarily kind to yourself. This is the kind of trial, when faith can help you through. Knowing in your heart that this child loves you and need you, whether or not you have access or not. Whether she can see her way to reach or, or not.
She is a child who has suffered and is suffering. So many of her feelings are compartmentalized, I believe, and she doesn't have consistent access to them. Likely she won't for a long time. This is consistent with her age. I think your sense that she have the same moral development as do you is not realistic. Her moral development is limited by her cognitive development. That is, her brain is not sufficiently developed to support her thinking as do you about her behavior or circumstances. She is a child afterall.
You serve her best by setting very, very firm limits, with direct and appropriate consequences. She should never again have access to your cards. Even if that means your hiding them in your car, when you are near her. And I agree with Nandina about trying to deny her access to that which she has purchased illegally.
I think this child is troubled and she needs help to deal with the circumstances of her life which is sad. While you cannot control whether or not she receives therapy, maybe you can help her access activities that involve caring and responsible adults, such as at a church or synagogue or the like, or hobbies such as dance, non-aggressive sports, camp, or art or drama, all of which could be outlets for her, to support her as she matures.
I know it is hard, but I would try to focus upon her develdopment and her needs as opposed to what she does wrong. What she has done wrong involving your cards, you have some responsibility for, for repeatedly creating conditions where she could do this, after you knew she would and could. I am not judging you. I am responsible in the same way with my own son. But you are on notice. The responsibility is yours.
Your plate is full. I am so sorry. You've always been there for this child, and have loved her and tried to protect her like nobody else in the world. Trust that. Believe that your love for her will carry her through. And just as important, that your love will carry you through.