Praise be to Allah.
You should convince this girl of the importance of hastening to embrace this great religion without delay, for Allah will not accept from anyone any religion but it. No one knows what will happen to him, and dying in a state of disbelief leads to loss in this world and the hereafter; in fact, remaining a disbeliever for one more moment is the utmost loss, ruin and deprivation. Congratulations to this girl for being convinced of Islam; now let her hasten to testify that there is no god but Allah and Muhammad is the Messenger of Allah, and let her not pay any attention to ill-thoughts and speculation, for this great religion does not burden its followers with anything more than they are able to bear. Allah, may He be exalted, says (interpretation of the meaning):
“On no soul does Allah place a burden greater than it can bear.”
“and has not laid upon you in religion any hardship”
“Allah intends for you ease, and He does not want to make things difficult for you”
If she becomes Muslim and is afraid that her family may harm her, she may conceal her Islam until Allah grants her relief and a way out. In that case, there is nothing wrong with her not wearing hijab and not doing whatever she is not able to do of religious duties; she may pray in secret and should not give up praying under any circumstances. She should fast if she is able to conceal her fasting, but she may break her fast if there is the fear that her being Muslim may be exposed, and she should make up those fasts during the year. She should have certain faith that Allah, may He be exalted, will grant her relief and a way out, for Allah does not forsake His slaves and does not abandon His beloved ones. He says (interpretation of the meaning):
“Is not Allah Sufficient for His slave? Yet they try to frighten you with those (whom they worship) besides Him”
With regard to marriage, she should refuse to marry any non-Muslim, giving any appropriate reason for that, and she should wait for relief from Allah. Perhaps Allah will guide her family, or she will find a Muslim whom she can marry and migrate with him far away from her homeland, or there may be some other option that Allah makes easy for her.
Whatever the case, it is not permissible for her to remain a disbeliever under any circumstances, and it is not permissible to delay becoming Muslim for any excuse. Rather she should enter Islam and do whatever she is able to, and strive her utmost; she should give precedence to religion over worldly concerns, and understand that she is not the first one to suffer or make sacrifices for the sake of her religion and pleasing her Lord. This is a well-travelled path, which many righteous women have travelled since Islam began and until today; women have sacrificed their wealth, their status, their families and even their lives for the sake of the religion in which they believe. Allah has told us the story of the people of the ditch, who gave precedence to the hereafter over this world, and they sacrificed themselves, regarding their lives as nothing for the sake of Allah. And He has told us the story of the magicians of Pharaoh, in whose eyes the pleasures and status of this world became insignificant, and they gave precedence to Paradise and forgiveness over all that this world contains. At the beginning of the day, they were disbelievers and evildoers, but at the end of the day they became righteous and pious men, and they said to Pharaoh:
“ ‘We prefer you not over the clear signs that have come to us, and to Him (Allah) Who created us. So decree whatever you desire to decree, for you can only decree (regarding) this life of the world.
‘Verily! We have believed in our Lord, that He may forgive us our faults, and the magic to which you did compel us. And Allah is better as regards reward in comparison to your (Firaun’s (Pharaoh)) reward, and more lasting (as regards punishment in comparison to your punishment).’
Verily! Whoever comes to his Lord as a Mujrim (criminal, polytheist, disbeliever in the Oneness of Allah and His Messengers, sinner, etc.), then surely, for him is Hell, therein he will neither die nor live.
But whoever comes to Him (Allah) as a believer (in the Oneness of Allah, etc.), and has done righteous good deeds, for such are the high ranks (in the Hereafter),
‘Adn (Edn) Paradise (everlasting Gardens), under which rivers flow, wherein they will abide forever: such is the reward of those who purify themselves ((by abstaining from all kinds of sins and evil deeds) which Allah has forbidden and by doing all that which Allah has ordained))”
O Allah, guide this girl, show her the way to You, grant her Your protection, keep her under Your care, and save her and her brother from the people who are given to wrongdoing.
And Allah knows best.