What is the ruling on a sister who is characterized by disobedience to her parents, drinking alcohol, engaging in relationships with foreign men, abandoning prayer, and possibly intending to leave Islam, and how should she be dealt with?

Your sister is in grave danger, as she has either apostatized or is on the verge of disbelief. It is obligatory upon you and her father to advise her, enjoin her to good, forbid her from evil, and prevent her from causes of corruption. For the father is responsible for his family before God. It is not permissible to leave her living alone while she is in this state. A Muslim should reside where he feels secure in his religion and his family, and should choose the country with the least corruption if he cannot find a country free of evils.