If she is afraid that it will be found out that she has become Muslim, how should she pray?

Firstly: 

We ask Allaah to help and guide this girl and to open her heart to Islam, and to fill her heart with the light of faith. We advise her to do that and not to hesitate, and to announce her Islam to her Lord, and to bear witness to the testimony of Islam, and to do whatever she can of its rituals. 

Secondly: 

The Muslim is obliged to offer the five prayers every day and night, and it is not permissible to omit any of them, no matter what one’s excuse, so long as one is of sound mind. 

If this girl cannot pray Maghrib, ‘Isha’ and Fajr for fear that her family may find out that she is Muslim, then she should not avoid praying, but she can do the following: 

1-Join Maghrib and ‘Isha’ at the time of the earlier or later prayer, and pray them in secret. Reciting out loud in the prayers in which Qur’aan is recited out loud, such as Fajr, Maghrib and ‘Isha’, is Sunnah, not obligatory. The same applies to raising the hands when saying the opening takbeer and when saying the takbeers when changing posture, and placing the right hand over the left when standing. All of these are Sunnah actions.

2-She may limit herself to doing the pillars and essential parts of the prayer. So she may recite al-Faatihah and not recite a soorah after it, and she may recite just one tasbeehah when bowing and prostrating. Thus she will be able to do the prayer in a few minutes. Girls are usually able to close the door of their rooms for a few minutes, such as when they change their clothes and the like, so she can do the prayer during that time.

3-If she wants to do wudoo’, she can do wudoo’ in the bathroom where no one can see her, as if she is relieving herself. If she is unable to do wudoo’ then she can do tayammum, even if she uses the wall or furniture of the house and prays with this tayammum.

4-If we assume that she cannot hide from her family even for a few minutes in which to pray, and she is afraid that if they find out she is Muslim she will suffer real harm, then it is permissible for her to pray whilst sitting, gesturing for the bowing and prostrating. If that is not possible then she may pray sitting and intending in her heart to bow and prostrate, whilst facing the qiblah. If she is unable to face the qiblah, then she may pray facing in any direction. If we assume that she can only pray whilst lying down, then she may do that. The point is that prayer is not waived for one who is accountable under any circumstances.

The basic principle concerning that is the verse in which Allaah says (interpretation of the meaning): “Allaah burdens not a person beyond his scope” [al-Baqarah 2:286] and the words of the Prophet (peace and blessings of Allaah be upon him): “Pray standing, and if you cannot then sitting, and if you cannot then on your side.” Narrated by al-Bukhaari (1117) and Abu Dawood (952). 

The fuqaha’ mentioned some cases in which the requirement to face the qiblah and bow and prostrate is waived, such as when fleeing from a wild animal or a flood or when fighting breaks out on the battlefield, when there is not enough time to do the prayer properly with all its essential parts. 

Ibn Qudaamah (may Allaah have mercy on him) said in al-Mughni (1/258): To sum up: if the fear is so intense that one cannot pray facing the qiblah or one needs to walk or is unable to do some of the essential parts of prayer, either because of permissible flight from an enemy, flood, wild beast or fire and the like, which one can only escape by fleeing, or when engaging in fighting the enemy or when fighting breaks out on the battlefield, and there is a need to charge and retreat and stab and strike and chase, then he may pray according to his situation, whether he is walking or riding, facing the qiblah if possible, or facing any other direction if that is not possible. 

If he is unable to bow and prostrate, he may gesture to indicate them, and lean forward more for prostration than bowing, according to what he is able to do. If he is unable to gesture, then it is waived. If he is unable to stand or sit and so on, then they are waived. If he needs to stab and strike and charge and retreat, he may do that. He should not delay the prayer until the time for it is over because Allaah says (interpretation of the meaning): “And if you fear (an enemy), perform Salaah (pray) on foot or riding” [al-Baqarah 2:239]. And Maalik narrated from Naafi’ that Ibn ‘Umar said: If the fear is greater than that, they may pray walking, standing on their feet, or riding, facing the qiblah or otherwise. Naafi’ said: I do not think that Ibn ‘Umar narrated it from anyone but the Messenger of Allaah (peace and blessings of Allaah be upon him). End quote. 

Indeed the fuqaha’ have stated that the prisoner or the one who is afraid that his being Muslim will be discovered should still pray. 

Ibn Qudaamah (may Allaah have mercy on him) said in al-Mughni (2/140): If he flees from an enemy in a permissible sense, or he flees from a flood or wild animal or fire, and he cannot escape it except by fleeing, then he may pray in the manner that is permitted in the case of extreme fear, whether he fears for himself or his property or his family. If a prisoner fears for his life if he prays, or if someone is hiding in a place, then they should pray however they are able to. This was stated by Ahmad with regard to the prisoner. If the one who is hiding is sitting and cannot stand, or he is lying down and cannot stand up or move, then he should pray according to his situation. This is the view of Muhammad ibn al-Hasan. Al-Shaafa’i said: He should pray and repeat it (later on), but this is not correct, because the one who is afraid should pray according to what he is able to do, and he does not have to repeat it, as is also the case for one who is fleeing. It makes no difference whether one is travelling or not, because what makes it permissible is fear of death, and that is the same in both cases. 

Whenever he can find a refuge to do his prayer, such as if the one who is fleeing from a flood can climb to a high place and the one who fears an enemy can enter a fortress where he will be safe from the enemy’s attack and from harm, then he should pray there then come out, and he does not have the right to offer the prayer of extreme fear, because that is only permitted in cases of necessity, so it is only to be done when necessary. End quote. 

To sum up: this girl has to offer the five prayers, and it is not permissible for her to omit any of them. But she may perform the prayer in whatever way she can, which includes offering the prayer of extreme fear if necessary. 

And Allaah knows best.