File a petition for guardianship. If the child is at least 14, she will have to nominate you in the petition. Notice must go out to the parents. Once guardianship is established, you can apply to Soc Sec. to be the representative payee on behalf of the girl. Please have a lawyer help you with the guardianship. It will go much smoother for you and the girl.
You go to the local district office of Social Security and apply to be the new payee. However, if the mother does not agree, then there is a problem since you are not the legal custodian of the child.
This response is meant to be information only and should not be considered to be legal advice. This information is not meant and should not be construed to be the formation of an attorney client relationship. I practice Virginia Workers compensation law and Social Security Disability law.
Obtaining a guardianship in Illinois is a fairly easy and inexpensive process. This would appear to be the first step. Perhaps this might be with the mother's consent. If successful, then the visit to Social Security would follow.
You may be able to get legal information at the legal aid office listed below:
Land of Lincoln Legal Assistance Foundation - Western Regional Office
310 Easton Street
Suite 330 Alton, IL 62002
The information provided here should not be construed to be formal legal advice. The provision of this general advice does not create a lawyer-client relationship. Persons with legal questions are encouraged to seek independent counsel for advice regarding their individual legal issues.