DM, you will drive yourself nuts trying to "diagnose" her and "figure it out." We just grasp at anything to make sense of the completely nonsensical behavior. I read countless books trying to understand drug and alcohol addiction. It was my attempt to control an uncontrollable situation.
It doesn't matter. Right now, what matters is behavior. If she has an addiction, you'll know soon enough because she won't be able to stop stealing (for whatever reason). So be very guarded. For a long time.
Addiction changes people, their personalities, their attitudes, their behaviors, their morals...EVERYTHING. They literally become different people than they were. And it doesn't matter what kind of addiction - drugs, alcohol, gambling... If your daughter has a shopping addiction, it will literally change her right before your eyes. Many addicts think in the beginning that they can "control it." When it controls them, they will do anything, hurt anyone, to get the "fix."
This is 100 percent true. Addiction causes the exact behavior you have been seeing. Our precious people that we love turn into monsters who will stop at NOTHING to get what they want. They will say anything and do anything to get more.
I often say that Addiction is a 40-foot-tall monster that mows down everything and everybody in its path. Our DCs are in the grip of the monster, and they won't shake him until they decide to start stopping and even then they will relapse time and again until they get the help they need to stop.
So again, go slow. Breathe and be guarded. Keep it simple---whatever you are requiring of her. I used to write three and four page contracts that were a joke. He had no intention of doing any of it, and finally, toward the end, I wrote a one-page contract and he tore it up in my face and walked out the door.
I hear that your daughter is behaving differently than that, and that is a good sign. Perhaps she is ready to change...now. I sure hope so.
But only believe what you can see. Talk is cheap.
Through it all, we are here for you and we understand the exhaustion, grief, disappointment and pain. Keep us posted.