What is the ruling of Islamic law and what is the advice that should be followed to deal with a sister who is 17 years old and refuses to adhere to religious teachings such as the hijab and prayer, befriends young men, prefers independence and living alone, and refuses marriage, knowing that her elder sister and her husband raised her?

There is no blame upon one who has exerted their utmost effort in upbringing if one of those under their care deviates. Blame is only upon the negligent. The practical options for dealing with this deviation are limited due to the disbelieving environment, the sister's age, which is nearly eighteen, and the relatives' refusal to host her. There is no effective option other than to continue to show affection towards her and gently persuade her with words to invite her to repentance or to move in with you. If that does not succeed, then continue to follow up with her and pray for her well-being, for this matter will not last long, and she will awaken from her heedlessness. So, be close to her when she returns. Continue trying to persuade her to return to your home and do not despair, and pray to Allah for her guidance and righteousness.