We would like to thank you for your efforts in spreading jurisprudential awareness. My question is about a girl who repeatedly swore by Allah that she would not return to a sin, but then she did return. She said that if she returned to the sin, she would disbelieve in her Lord, and she did return. Has she disbelieved by returning to the sin? If she has disbelieved, what must she do to return to Islam?

All praise is due to Allah, and peace and blessings be upon the Messenger of Allah, and upon his family and companions.

This girl does not become an unbeliever by her words. She must repent sincerely, seek forgiveness, and perform righteous deeds. Abstaining from sins is achieved by realizing faith and fearing the Most Merciful, not by mere words and oaths. The questioner should remind her friend of Allah, with both encouragement and warning, and help her to follow the path of guidance. If her sin is related to mixing with non-mahram (definition) men, then she should strive to get married. And Allah knows best.