How to become a Legal guardian over my cousin while her parents are in jail?

I have a 9 year old cousin who's parents are in jail. I have been taking care of her. I am sick and been in and out of the hospital now my aunt wants to take her from me. How do I become her legal guardian while her parents are in jail?How to become a Legal guardian over my cousin while her parents are in jail?
You would apply in family court by filing a motion with all your documentation that you are the one who is taking care of her while her parents are in prison..you may want to consult a lawyer due to the facts this is not your child..