What is the ruling on a girl marrying herself if her parents are polytheists and the judge is not Muslim and does not rule by Islamic Sharia? And how can an individual become a Sharia judge?

Marriage is not valid except with a guardian (wali), based on the Prophet, peace and blessings be upon him, saying: "There is no marriage except with a guardian," and his saying, peace and blessings be upon him: "A woman may not marry off another woman, nor may a woman marry herself off." Among the conditions for a guardian is Islam. If the father is a disbeliever, guardianship transfers to the next closest male relative, and so on. If there are no such relatives, or their guardianship is forfeited, then the Muslim ruler is the guardian for one who has no guardian. If there is no guardian or ruler, she may entrust her affairs to a just man to marry her off from him.