Sounds like she is hanging out with a bad influence. How was your relationship before this stuff started? When I was that age I started to hang out with a girl who had a lot of issues. She stole from her mom, and I thought she was cool so I did it a couple times. Luckily I became friends with another girl, who was a much better influence. Check on her friends, maybe she is being influenced. By the way that bad friend also introduced me to drugs, so be aware.
My feeling is that she is upset about something and is acting out, so check on what has been happening her life could make her unhappy , could be she is seeking attention, negative attention is better than none. Does hse say whyy she takes these things? is school going well , any new Family ,any new happenings could make her feel insecure.