Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
It is not permissible for a Muslim to marry a non-Muslim, except if she is among the People of the Book, i.e. a Christian or a Jew. For this marriage to be valid, the woman has to be chaste; the evidence is the Saying of Allah: {Made lawful to you this day are AtTayyibât [all kinds of Halâl (lawful) foods, which Allâh has made lawful (meat of slaughtered eatable animals, etc., milk products, fats, vegetables and fruits, etc.). The food (slaughtered cattle, eatable animals, etc.) of the people of the Scripture (Jews and Christians) is lawful to you and yours is lawful to them. (Lawful to you in marriage) are chaste women from the believers and chaste women from those who were given the Scripture (Jews and Christians) before your time,…}[5:5].
Therefore, if the said woman is a Christian or a Jew, then the marriage is correct, and the rulings about marriage apply to them. If for instance she hates her husband and the social relations between them had become impossible, then she can ask for divorce from him, if he accepts then there is no problem. However, if he refuses, she can suggest giving him an amount of money in exchange of him divorcing her. If she is harmed by staying with him, then she can take the matter the Islamic courts, which can grant the divorce on his behalf. However, if the woman is an atheist or upon any kind of disbelief, then it is not valid for a Muslim to marry her in the first place and she does not need a divorce to be separated from him. If your marriage is in the last category and it is registered in the legal system then you can seek redress through the courts, because Islam does not recognize such a marriage.
Allah knows best.