We praise Allah, may He be exalted, for having guided our dear sister to Islam and enabled her to pray and fast. We ask Allah to bless her with steadfastness and strength and to guide her family and relatives.
It is not permissible for a Muslim woman to marry a Christian man, and this is not regarded as a marriage; rather it is zina (fornication or adultery) and immoral conduct. She has to refuse to do that by all possible means, and hasten to announce her Islam in her official documents. She can seek help in doing that from experts such as lawyers and the like. If announcing her Islam will result in her mother cutting her off, or becoming ill, or even dying, there is no sin on her for that, because she will have done what is required of her, and obeying Allah and pleasing Him takes precedence over obedience to anyone else. The matter is very serious; it is the matter of kufr (disbelief) or eemaan (faith), so there is no room in this case for emotion. Perhaps by declaring her Islam, that will pave the way for her father and mother to become Muslim, even if that is after a while. The point is that her remaining steadfast in Islam is what is obligatory and essential. There is nothing beyond that except apostasy and loss. It is not permissible for her under any circumstances to marry a Christian man. She has to hasten to confirm her Islam according to regular official procedures, then she should be gentle in announcing that to her family, and she should seek the help of people who are experienced and skilled in dealing with such matters. If announcing her Islam results in her family cutting her off or becoming ill, she is not responsible for any of that.
We think that the general circumstances now will be more helpful in dealing with this matter than was the case previously. We ask Allah to give her the joy of seeing her family being guided to Islam.
We should point out that the correct thing to say would be I have a friend who was Christian, because now she is a Muslim. The fact that she has delayed announcing her Islam does not mean that she has not become Muslim. The one who utters the Shahaadatayn in a serious manner has entered Islam, and is required to pray and do all other obligatory deeds, and she has done that, praise be to Allah.
And Allah knows best.
Reproduced from Islam QA