Help unusual situation

I have an unusual situation. I was dating a man that was separated and had a child. The biological mom left the child in Thailand with the grandparents. Eventually they got divorced and he got custody of the child. We moved her in with us when she was 4 years old. We never did marry. When she was 10 her dad died. Her mom agreed to let the child stay with me until after Christmas. Something happened and her mom asked if she could stay until the end of the school year. She is now 14 and still with me. In my eyes she is my daughter, but legally I know she is not. She introduces me as her step mom and her mom is very supportive of me raising her. She visits her mom 3 or 4 times a year. She talks to her frequently on the phone. I want to adopt her so I can have a legal say over her. If, god forbid, something was to happen to her. I need to get her health insurance and such. I live in Az and do not know the laws or what to do. Can she have 2 legal moms? Any advice would be appreciated.