Your sister will be able to get some form of control over your father's assets and estate but I cannot answer with certainty based on the ambiguity in your question. A durable power of attorney is a document a person gives to another authorizing them to act on their behalf, just as an attorney. Your father certainly can execute one in favor of your sister.However, I sense your question is more concerning a guardianship over your father due to health or medical issues. If this is the case, your sister can get a guardianship over your father if it is declared that he is unable to manage his personal and financial affairs. It is a complex legal proceeding but it is available to anybody who was a resident of New Jersey, whether or not you were born here.