Hello Ashley,
Further to respond re: what you said at the end of your question about the quick changes in your stepdaughter from one minute to the next.
Please read up about bi-polar so you are aware of the manifestations, as mental illnesses have a genetic component. I'm not a professional so can't diagnose mental health conditions, however, I do want you to know that bi-polar can develop in children at early ages. My friend's daughter started going through her condition when she was eight years old.
So educate yourself and be proactive should something happen that resembles what happened to her mother. I'm not saying that something could definitely happen. However, your stepdaughter's mother has bipolar so you should know about this illness if only to understand how it effects the mother.
Lastly and again, be strong and reinforce the positive behavior.
Regards,
Christina