Should she go ahead with this marriage or not?
If your cousin is righteous and adheres to his religion, prays regularly and is of good character, then do not hasten to seek a separation. Many minor differences can be dealt with and an understanding can be reached. It may need some time in order to get used to one another and become comfortable with one another. But the most important matter is his relationship with his Lord, may He be glorified and exalted, and his adherence to his religion. The one who is religious will help his family to obey Allaah and will being them closer to pleasing Allaah. Such a person is usually trustworthy, for his religious commitment will prevent him from mistreating his family or being unjust, especially if you travel with him and go to live far from your family. But if he is careless with regard to his religious commitment and does not pray regularly, and is not known to be righteous and upright, then undoubtedly marriage to him is a dangerous matter, because the one who is negligent towards his religious commitment will be more negligent in other matters; if a person neglects the rights of his Lord and Creator, it will come as no surprise that he neglects the rights of others. Leaving one who is like this now is better than leaving him later, before the marriage is consummated and any children are born.
You have to pray istikhaarah, for the one who seeks guidance from his Lord and prays istikhaarah cannot lose. And consult righteous people among your family who know about your husband and his character and nature.
You should strive to equip yourself with the best of characteristics and attitudes, for both spouses are enjoined to do that. The problem may also be due to you as well. Perhaps your husband has complaints about your attitude and behaviour just as you have about his. We ask Allaah to set your affairs straight and to make good easy for you wherever it is.
In your question you say "fate decreed". This is a grave error, for fate has no will. What you should say is "Allaah willed" or "Allaah decreed".
Shaykh Ibn 'Uthaymeen (may Allaah have mercy on him) was asked about saying, "circumstances dictated that such and such should happen" or "fate decreed that such and such should happen."
Saying "fate willed" or "circumstances willed" are reprehensible phrases, because circumstances or time have no will, and fate has no will. Rather the One who wills and decrees is Allaah, may He be exalted and glorified. It would be better for a person to say: "The decree of Allaah dictated that such and such should happen." There is nothing wrong with that. But it is not permissible to attribute will to fate. End quote.
Majmoo' Fataawa Ibn 'Uthaymeen, 3/113
And Allaah knows best.