My niece is 17. Her mother ( my sister) is deceased. She lived with me for a while as per her mother's request. Her parents were never married. After my sisters death the father sued for custody. She lived with him for about 1.5 years but has lived with me for 10 months. Her dad provides no support. No insurance, nothing. Can I file for sole custody?

When will she turn 18? Why did you allow her to move in when the father was awarded custody? Do you realize he might be able to sue you for parental interference?

You have no legal right for her to live with you! You can't authorize medical care, schooling etc.

Depending in when she turns 18 it will probably take too long to get custody.