Yes, but difficult.
Unfortunately, in the majority of cases, she will get bounced around foster care. You will need to file a challenge in court to get the girl.
That would depend on a lot of factors, including the age of the niece. In general, it would need to be shown that whoever was raising her now was abusive or neglectful or in some manner not in her best interest's. Then it would have to be shown that the Aunt would be better - than any other relative the niece may have. And even then, still might not be awarded the niece, the State may find that foster care would be better. You must consult with an attorney in your area that specializes in custody matter. Explain the details to him, so that you can receive advice specific to your situation.
you will have to file papers and you will need right home.
You have to go to court and petition for custody. Unless her parents are unfit you will not get custody though.
File a motion for full guardianship of a child in need of care.
file a child in need of care motion.
it depends ifyou currently have custody of your grandchildren already. if you do then you must go through an adoptiion. otherwise most states wont grant fulll custody. grandparents used to have what they call grandparents rights but many grandparents abused that right so now a child must go through foster care and the courts.
You file an emergency child in need of care and custody in court. See link to learn how.
You have to file a child in need of care motion in the other state.
File a child in need of care motion
If there's a valid reason, they have to file a motion for a child in need of care with the court.
File a motion for custody based on possession. see link