What can I do or say to help my fiancée wear the hijab, given that the decision is hers alone, and I do not want to force her?

A Muslim man must marry a religious, chaste, and veiled woman. The hijab is obligatory for women as it protects them and society.

If a woman is religious and of good character but falls short in wearing the hijab, there is no harm in marrying her after inviting her to wear it and her committing to it. This is because the husband is responsible for his wife and must enjoin her to do good and forbid her from doing evil.

A woman who does not wear the hijab must be reminded of obedience to Allah and His Messenger, and that the hijab is a divine command in the Holy Quran, and that not adhering to it is an act of disobedience that leads to the corruption and alteration of the heart. The noble Hadith also warns against "women who are dressed yet naked" (kasiyat ariyat) who will not enter Paradise.

It is not permissible to engage in a relationship with a non-mahram woman, even with the intention of marriage, due to the forbidden acts it may lead to. A successful marriage is built upon obedience to Allah.

You must end this relationship with the woman and invite her to adhere to the hijab and steadfastness in obedience through righteous women.