It goes without saying that the relation between the spouses should be based on tranquility, love, and mercy. It is the duty of both the husband and wife to act as a source of comfort and tranquility for each other. They should do what they can — physically, emotionally, and spiritually — to make each other feel happy and comfortable. They must care for each other. They should not inflict any physical or verbal injury whatsoever on each other.
A husband is not allowed to torture his wife or abstain from divorcing her to increase her harm. So, it is our duty to advise a person who is found of torturing his wife to fear Allah. He should respect his wife and stop beating her. He should either work on resolving the differences in a good manner or divorce his wife and leave her in peace.
Sheikh Ahmad Kutty, an Islamic scholar, stated while responding to a question, of this nature,
If her husband is abusive toward her and she has no hope that he will ever change, then she has every right to seek divorce from him. If he refuses to grant her divorce, she can obtain it through legal and Islamic channels. In other words, she is perfectly justified in seeking a legal divorce on that ground. If she were to do so, then the divorce thus obtained would be validated as Islamic by the imam of the Islamic center or mosque in the area, if they are living in North America or anywhere in Europe where she has no recourse to Islamic courts.
According to authentic scholars and jurists who are versed in the Islamic fiqh (jurisprudence) of minorities, the court’s divorce — as long as it has been justified in Islam — can be validated from an Islamic viewpoint by the imam of the mosque, who is duly qualified in Islamic jurisprudence and has the license to solemnize marriages.
Let it be known that Islam does not tolerate spousal abuse of any kind, whether physical or emotional, for Allah orders the husbands in the Qur’an to deal with their spouses kindly. Almighty Allah says, (And consort with them [you wives] kindly; then if you hate them, it may be that you dislike a thing while Allah has placed abundant good in it) (An-Nisaa’ 4:19).
The above order of consorting with one’s wife in a goodly manner has been interpreted by Imam Al-Qurtubi as obliging husbands to observe the highest standards of decency and humanity toward their wives. Hence, no wife should be made to go through torture or abuse. Furthermore, Allah gives husbands one of two legitimate options if they find themselves locked up in quarrels: (When you have divorced women and they have reached their term, then retain them in kindness or release them in kindness, and do not retain them to their hurt so that you transgress [the limits], and he who does that has wronged his own soul) (Al-Baqarah 2:231).
So, there is no third option — namely, to hold the wife as a prisoner in an abusive relationship. Accordingly, your friend is undoubtedly holding his wife as a prisoner in a marriage that neither he nor she is able to maintain according to the way Allah has ordered.
It is therefore permissible for her to seek whatever legal channels at her disposal to come out of such an abusive marriage. She can get the legal divorce, which can then be validated from an Islamic perspective.