Single Mother, who gets custody if I die?

I am a single mother living in North Carolina. My daughter is 6 years old now. Her father has never met her and has no interest in us at all. I don’t know where he is. He does not pay child support or have visitation of any kind. I haven’t even spoken with him since I got pregnant. I am really not concerned about him wanting custody. My larger concern is that my daughter not end up in the Social Services system.
I have very little family and want to make sure my daughter ends up with my sister and her husband if I were to die while she is a minor. My sister would seem the only logical choice from a legal standpoint as well (There really isn’t anyone else.), but I want to be as sure as possible.
Is there a document I can complete now that would help? Is this something I could specify in a will or similar? If so, how would it hold up in practice?

Thank you in advance for any insight you can provide.

If the father has not been involved in the child’s life, has no connection to her, and is not listed on the birth certificate you may appoint your sister as legal guardian in your willl.

If the father has not been involved in the child’s life, has no connection to her, and is not listed on the birth certificate you may appoint your sister as legal guardian in your willl.