child support

north carolina-
i have a niece (age 17) which i'm responsible for custody/ financial wise. court papers allow me to retain custody if needed, she lives with another family.its an equitable situation. also i'm responsible for her financial responsibilities. she inherited some money upon my parents death. the reason i/we are in this situation is because (my sister, her mother) is also deceased, and her biological father is a non compliant child support payer. he hasn't made payments in a long while, and i have been to court, but nothing i seem to do court wise gets him to pay. my question is, since the money she inherited was due to my families work, can i get her to sign a legal document stating that if something were to happen to her the money she inherited would come back to my side of the family and not to her fathers, since iam the sole beneficiary or only child left. because i don't want that money going to her biological father, since he has been non existant in her life. and has failed to be a father. would this be possible particularly is she consents? and based i assume on her being a legal age, because she will be 18 next july.