What is the ruling on a girl's relationship with a man as an 'urfi husband, while she is married to another man whom she did not desire? And what should she do concerning each of the two husbands?

What is called an 'urfi marriage is an agreement between a man and a woman to marry without fulfilling the conditions of a valid marriage, such as the presence of a guardian (wali) and two witnesses. This is not a legitimate marriage; rather, it is considered a form of fornication (zina). You must sever your relationship with this man and repent to Allah, and accept whoever your guardians choose as a husband, remembering His (Allah's) saying: ﴿And it may be that you dislike a thing which is good for you and that you like a thing which is bad for you. Allah knows but you do not know.﴾ (Al-Baqarah: 216). If it becomes difficult to live with your legitimate husband, you may seek khul' (divorce at the wife's instance).